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Max Planck Encyclopedia of Public International Law [MPEPIL]

Maritime Delimitation in the Caribbean Sea and the Pacific Ocean and Land Boundary in the Northern Part of Isla Portillos Cases

Christine Pichel

Content type:
Encyclopedia entries
Product:
Max Planck Encyclopedias of International Law [MPIL]

Module:
Max Planck Encyclopedia of Public International Law [MPEPIL]
Article last updated:
December 2024

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2023. All Rights Reserved.date: 23 April 2025

Subject(s):
Sovereignty — Continental shelf — Exclusive economic zone — Islands and artificial islands — Baselines — Delimitation — Territorial sea — UNCLOS (UN Convention on the Law of the Sea) — Treaties, interpretation — Boundaries

Published under the auspices of the Max Planck Institute for Comparative Public Law and International Law under the direction of Professor Anne Peters (2021–) and Professor Rüdiger Wolfrum (2004–2020). 

Original version by Christine Pichel January 2019; updated by Christine Pichel December 2024.

A.  History of Proceedings

1  On 25 February 2014, Costa Rica instituted proceedings against Nicaragua before the International Court of Justice (ICJ) in respect of a dispute concerning ‘the establishment of single maritime boundaries between the two States in the Caribbean Sea and the Pacific Ocean, respectively, delimiting all the maritime areas appertaining to each of them’ (Maritime Delimitation in the Caribbean Sea and the Pacific Ocean (Costa Rica v Nicaragua) (Application) para. 3 (‘Case Concerning Maritime Delimitation’)).

2  On 16 January 2017, Costa Rica instituted proceedings against Nicaragua before the ICJ in respect of a dispute concerning ‘the precise location of the land boundary separating the Los Portillos/Harbor Head Lagoon sandbar from Isla Portillos’ and ‘the …establishment of a military camp by Nicaragua on the beach of Isla Portillos (Land Boundary in the Northern Part of Isla Portillos (Costa Rica v Nicaragua) (Application) para. 3 (‘Case Concerning the Northern Part of Isla Portillos’)). In its application, Costa Rica also requested that the Court join the new proceedings with the proceedings in the Case Concerning Maritime Delimitation.

B.  Joinder of Proceedings

3  Upon request for a joinder of the proceedings from Costa Rica, by an Order of 2 February 2017, the ICJ decided to join the two proceedings in the Case Concerning Maritime Delimitation and the Case Concerning the Northern Part of Isla Portillos on the basis of Article 47 Rules of Court (Joinder of Cases and Proceedings). The Court then recalled that this provision leaves the Court a ‘broad margin of discretion’ ((Order) para. 16) to join the proceedings in two or more cases. In this respect, the Court also noted that the exercise of this power to join proceedings has been applied by the Court, or its predecessor, in cases where the joinder was in harmony with the principle of the sound administration of justice and the need for judicial economy.

4  In view of the above, the Court considered that the two cases should be joined since there was a close link between the claims made by Costa Rica in the Case Concerning the Northern Part of Isla Portillos and certain aspects of the dispute in the Case Concerning Maritime Delimitation. The Court also observed that the joinder would allow it to simultaneously deal with all the interrelated issues raised by the parties, including questions of fact or law that were common to both cases.

C.  General Background

1.  Geography

5  Costa Rica and Nicaragua are situated in Central America. Both countries share a land boundary that spans from the Caribbean Sea to the Pacific Ocean. Nicaragua lies to the north of that boundary and Costa Rica to the south.

6  Isla Portillos is an area of approximately 17 km2 that is bounded to the west by the San Juan River and to the north by the Caribbean Sea; its northern part is the subject of the land boundary dispute in the present joined cases. At the northwestern extremity of Isla Portillos, a sandspit of variable length deflects the final course of the San Juan River. On the coast of Isla Portillos, at approximately 3.6 km east of the mouth of the San Juan River, a lagoon called Laguna Los Portillos by Costa Rica and Harbor Head Lagoon by Nicaragua is located. This lagoon is separated from the Caribbean Sea by a sandbar.

7  On the Pacific side, the coast of Nicaragua is relatively straight and generally follows a north-west to south-east direction. The coast of Costa Rica is more sinuous and includes the peninsulas of Santa Elena (near the land boundary terminus), Nicoya, and Osa.

2.  Historical Context

8  On 15 April 1858, Costa Rica and Nicaragua signed a Treaty of Territorial Limits (‘1858 Treaty’) whereby the two countries fixed the course of the land boundary between them from the Pacific Ocean to the Caribbean Sea.

9  On 24 December 1886, following challenges by Nicaragua to the validity of the 1858 Treaty (Treaties, Validity), Costa Rica and Nicaragua signed another instrument by which the question of the validity of the 1858 Treaty was submitted for arbitration to the President of the United States of America, Grover Cleveland. Additionally, both countries asked the President to decide upon all the other points of doubtful interpretation raised by either party in relation to the treaty. The Award in Regard to the Validity of the Treaty of Limits between Costa Rica and Nicaragua of 15 July 1858 (‘Cleveland Award of 1888’) confirmed the validity of the 1858 Treaty and found that the boundary line on the Atlantic side began ‘at the extremity of Punta Castilla at the mouth of the San Juan de Nicaragua River, as they both existed on the 15th day of April 1858’ (Maritime Delimitation in the Caribbean Sea and the Pacific Ocean (Costa Rica v Nicaragua) and Land Boundary in the Northern Part of Isla Portillos (Costa Rica v Nicaragua) (Judgment) para. 52 (‘2018 Judgment’), citing the Cleveland Award of 1888 para. 3(1)).

10  On 27 March 1896, subsequent to the Cleveland Award of 1888, the parties signed the Convention on Border Demarcation Concluded between the Republic of Costa Rica and the Republic of Nicaragua, by which they agreed to establish two national Demarcation Commissions. The parties also agreed, in the same instrument, that the Commission would include an engineer, appointed by the President of the United States of America, who ‘shall have broad powers to decide whatever kind of differences may arise in the course of any operations’ and ‘whose ruling shall be final’ (2018 Judgment para. 53, citing Art. II of the 1896 Convention). The United States General Edward Porter Alexander, who was so appointed, rendered five Awards.

11  On 30 September 1897, General Alexander determined, in his First Award, the starting segment of the land boundary on the Caribbean Sea side taking into consideration the geomorphological changes that had occurred since 1858.

12  On 18 November 2010, Costa Rica instituted proceedings against Nicaragua before the ICJ in respect of a dispute concerning certain activities carried out by Nicaragua in the Border Area (Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v Nicaragua) and Construction of a Road in Costa Rica Along the San Juan River (Nicaragua v Costa Rica) (‘Case Concerning Certain Activities’)). In its 2015 Judgment, the Court found that Costa Rica had sovereignty over the ‘disputed territory’, meaning:

the northern part of Isla Portillos, that is to say, the area of wetland of some 3 square kilometers between the right bank of the disputed caño, the right bank of the San Juan River up to its mouth at the Caribbean Sea and the Harbor Head Lagoon (para. 69).

13  However, the Court also noted in its description of that area that it did not specifically refer to:

[T]he stretch of coast abutting the Caribbean Sea which lies between the Harbor Head Lagoon, which lagoon both Parties agree is Nicaraguan, and the mouth of the San Juan River (ibid. para. 60).

D.  The Judgment of 2 February 2018

1.  Subject-matter of the Dispute

14  In the Case Concerning Maritime Delimitation, the dispute concerns the delimitation of the single maritime boundary between Costa Rica and Nicaragua in the Caribbean Sea and the Pacific Ocean with respect to the territorial sea (‘TS’), the exclusive economic zone (‘EEZ’), and the continental shelf (‘CS’).

15  In the joined Case Concerning the Northern Part of Isla Portillos, the dispute concerns the course of the land boundary in the northern part of Isla Portillos. In particular, the precise location of the land boundary separating both ends of the Los Portillos/Harbor Head Lagoon sandbar from Isla Portillos. Furthermore, the dispute also concerns the establishment of a new military camp on the beach of Isla Portillos by Nicaragua.

2.  Jurisdiction

16  The Court noted that Costa Rica had invoked, as bases of jurisdiction for both cases, the declarations by which Costa Rica and Nicaragua have recognized the compulsory jurisdiction of the Court under Article 36(2) and (5) Statute of the Court, respectively, as well as Article XXXI American Treaty on Pacific Settlement (1948), known as the Bogotá Pact (1948). The Court also noted that Nicaragua did not contest the Court’s jurisdiction to entertain Costa Rica’s claims. (See International Court of Justice, Optional Clause; International Courts and Tribunals, Jurisdiction and Admissibility of Inter-State Applications).

17  In view of the above, the Court found that it had jurisdiction over the disputes in the joined cases.

3.  Merits

(a)  Land Boundary in the Northern Part of Isla Portillos

(i)  Issues Concerning Territorial Sovereignty

18  The Court first noted that there were issues of territorial sovereignty that needed to be examined since they could have an impact on the maritime delimitation on the Caribbean Sea side.

19  Costa Rica contended that the issue of sovereignty over the ‘beach of Isla Portillos’ was settled by the Court in its 2015 Judgment in the Case Concerning Certain Activities. This was because the term ‘disputed territory’ included ‘the beach of Isla Portillos’ (2018 Judgment para. 61). Therefore, the decision possessed the force of res iudicata (ibid.). The Court then clarified that in its 2015 Judgment the question of sovereignty regarding the coast of the northern part of Isla Portillos was expressly excluded by the parties and thus the Court did not take a decision on that issue (ibid. para. 69).

20  The Court then noted that according to the assessment of the court-appointed experts, which was not challenged by the parties, the configuration of the coast of Isla Portillos had undergone significant geomorphological changes since the time of the Alexander Awards and the work of the Demarcation Commissions. In this respect, the experts particularly observed that the former water channel connecting the San Juan River with Harbor Head Lagoon had disappeared due to coastal recession. In view of these findings and considering the present configuration of the coast of Isla Portillos on the issue of territorial sovereignty, the Court determined that Costa Rica had sovereignty over the whole of Isla Portillos up to where the San Juan River reaches the Caribbean Sea.

21  As for the Los Portillos/Harbor Head Lagoon, the Court recalled that as stated in its 2015 Judgment, the parties had agreed that Nicaragua has sovereignty over Harbor Head Lagoon. The Court also noted that Costa Rica requested the Court, in the present case, to determine that the sandbar separating the Lagoon from the Caribbean Sea is part of the Nicaraguan territory in the area of Isla Portillos insofar as this sandbar remained above water at all times.

22  The Court determined, in the light of the assessment made by the court-appointed experts in the present joined cases, which was not challenged by the parties, that the sand barrier separating the Lagoon from the Caribbean Sea remained above water even at high tide. Therefore, the Court concluded that the parties also agreed that the sandbar is under Nicaragua’s sovereignty.

23  Consequently, the Court concluded that Costa Rica had sovereignty over the whole of Isla Portillos except the enclave of Harbor Head Lagoon and the sandbar separating it from the Caribbean Sea, over which Nicaragua has sovereignty. (See Enclaves).

(ii)  Starting Point of Land Boundary on the Caribbean Sea Side

24  In the light of its 2015 Judgment and its findings in the present joined cases, the Court concluded that the starting point of the land boundary is the point at which the right bank of the San Juan River reaches the low-water mark of the coast of the Caribbean Sea. Taking into consideration the present configuration of the coast, the Court determined that this point was situated at the end of the sandspit constituting the right bank of the San Juan River at its mouth.

(iii)  Course of the Land Boundary for the Enclave of the Harbor Head Lagoon

25  In view of the expert’s assessment, the Court concluded that the sandbar extended between the points located at the north-eastern and north-western ends of the Lagoon, currently between points Ple2 and Plw2, as identified by the experts, respectively. The Court thus concluded that from each of these points, the land boundary should follow the shortest line across the sandbar to reach the low-water mark of the coast of the Caribbean Sea.

(iv)  Installation of a Military Camp on Costa Rican Territory

26  Costa Rica claimed that Nicaragua had violated Costa Rica’s sovereignty and territorial integrity as well as the 2015 Judgment of the Court in the Case Concerning Certain Activities by ‘establishing and maintaining a new military camp on the beach of Isla Portillos’ (2018 Judgment para. 74). (Territorial Integrity and Political Independence).

27  The Court first noted that, according to the expert’s assessment, the place where the military camp was located lay on the west of the north-western end of the Harbor Head Lagoon (2018 Judgment para. 77). In view of its decision regarding the land boundary for the enclave of the Harbor Head Lagoon, the Court then observed that the military camp was installed on Costa Rica’s territory since the camp was placed on the beach close to the sandbar, as defined by the Court in its present judgment, but not on it (ibid.). Accordingly, the Court concluded that Nicaragua had violated the sovereignty of Costa Rica by establishing and maintaining a military camp on Costa Rican territory (ibid.). In consequence, the Court ordered Nicaragua to remove its military camp from Costa Rican territory (ibid.).

(b)  Maritime Delimitation in the Caribbean Sea

(i)  Starting Point of the Maritime Delimitation

28  The Court first noted that the starting point of the maritime boundary would normally be the starting point of the land boundary at the end of the sandspit bordering the San Juan River where the river reaches the Caribbean Sea. However, considering the great instability of the coastline in the area of the mouth of the San Juan River, as indicated by the experts, the Court observed that it was not possible to identify on the sandspit a fixed point that would be ‘suitable’ (2018 Judgment para. 86) as the starting point for the maritime delimitation on the Caribbean Sea side.

29  Consequently, the Court selected a fixed point at sea connecting it to the starting point on the coast by a mobile line. Since the coastline at the mouth of the San Juan River is receding due to erosion from the sea, the Court considered that it was appropriate to place that fixed point at sea at a distance of 2 nautical miles (‘nm’) from the coast on the median line.

(ii)  Delimitation of the Territorial Sea

30  The Court considered that Article 15 United Nations Convention on the Law of the Sea (‘UNCLOS’) is the law applicable to the delimitation of the TS (Applicable Law; Applicable Law: Dispute Settlement under the United Nations Convention on the Law of the Sea (UNCLOS)). Accordingly, the Court first proceeded to draw a provisional ‘median line’ (2018 Judgment para. 90) and then considered whether any special circumstances existed which justify adjusting that ‘equidistance line’ (ibid.).

31  With regard to the base points, the Court constructed the provisional median line on the basis of salient points situated on the natural coast and located on solid land since they have a relatively higher stability than points placed on sandy features. However, the Court decided that Paxaro Bovo and Palmenta Cays, features used by Nicaragua to place base points, would not affect the construction of the equidistance line.

32  The Court then considered whether, as claimed by Nicaragua, the combined effect of the concavity of Nicaragua’s coast west of the mouth of the San Juan River and of Costa Rica’s coast east of the Harbor Head Lagoon constitutes a special circumstance for the purposes of the delimitation of the TS. In this regard, the Court concluded that this effect was of limited significance and therefore it could not be considered as a special circumstance justifying the adjustment of the equidistance line.

33  However, the Court observed that the sandspit near the mouth of the San Juan River was highly unstable and narrow. The Court then considered that this constituted a special circumstance affecting the delimitation of the TS on the Caribbean Sea side. Consequently, the Court determined that the fixed point at sea on the median line be connected by a mobile line to the closest point on solid land to the mouth of the San Juan River on Costa Rica’s coast.

34  The Court further observed that although this point on solid land had been identified by the experts as point Pv with specific coordinates, it was likely to move over time due to geomorphological changes. The Court then concluded that, for the present, the fixed point at sea should be connected to the point on the low-water mark of the coast of the Caribbean Sea which is closest to the point identified by the experts as Pv.

35  The Court then determined that from the fixed point at sea the delimitation line for the TS would follow the median line as constructed using the base points selected in relation to the present configuration of the coast.

36  Regarding the sandbar separating Harbor Head Lagoon from the Caribbean Sea, the Court noted that the sandbar was ‘a minor feature without vegetation and characterized by instability’ (2018 Judgment para. 89). Although the Court then considered that the instability of the sandbar and its situation as a small enclave within Costa Rica’s territory was a special circumstance relevant for the delimitation of the TS, the Court determined that this feature would not have any effect because of its particular characteristics:

Should territorial waters be attributed to the enclave, they would be of little use to Nicaragua, while breaking the continuity of Costa Rica’s territorial sea. Under these circumstances, the delimitation in the territorial sea between the Parties will not take into account any entitlement which might result from the enclave (2018 Judgment para. 105).

37  The Court then described in paragraph 106 of its judgment the maritime boundary line in the TS as the line obtained by joining the point on solid land on Costa Rica’s coast that is closest to the point Pv with the fixed point at sea and by joining this last point with geodetic lines with points A to L. The Court also fixed the endpoint of the delimitation of the TS at point Lx with specific coordinates.

(iii)  Delimitation of the Exclusive Economic Zone and the Continental Shelf

38  The Court first noted that the parties asked the Court to delimit their respective EEZ and CS drawing a single delimitation line. The Court also noted that Articles 74 and 83 UNCLOS are the law applicable to the delimitation of these areas, respectively.

39  As a first step, the Court proceeded to identify the relevant coasts and the relevant area. In this respect, the Court observed that the entire mainland coast of Costa Rica and the mainland coast of Nicaragua up to Punta Gorda (north) where the coast shows a significant inflexion are relevant. This is because these coasts generate projections that overlap with projections from the other Party’s coast.

40  With regard to the coasts of the Corn Islands and of the Cayos de Perlas (belonging to Nicaragua), the Court decided that the coasts of the Corn Islands that do not face north needed to be included in the length of Nicaragua’s relevant coasts. However, since Nicaragua did not prove the capacity of this feature to ‘sustain human habitation or economic life of their own’ as required by Article 121 UNCLOS and therefore their capacity to generate maritime projections, the Court considered that their coasts should not be taken into consideration.

41  The Court then concluded that the total length of the coasts was 228.8 km for Costa Rica and 465.8 km for Nicaragua, with a ratio of 1:2.04 in favour of Nicaragua.

42  With regard to the relevant area, the Court recalled that it includes the part of the maritime space in which the potential entitlements of the parties overlap. Therefore, the relevant area cannot extend to areas in which either Party has no entitlement either because of an agreement it has concluded with a third state or because that area lies beyond a boundary determined by a court or tribunal between that Party and a third state (2018 Judgment para. 117, citing Territorial and Maritime Dispute (Nicaragua v Colombia) (Judgment) para. 163 (‘2012 Judgment’)).

43  Accordingly, the Court considered that, except for the spaces attributed to Colombia on the basis of the 2012 Judgment, the relevant area in the north includes the whole maritime space situated within a distance of 200 nm from Costa Rica’s coast. However, the Court noted that, in the south, for the purpose of the approximate identification of overlapping entitlements of the parties to the present case, the spaces where third states have a claim may be included, but without the Court pronouncing itself on such claims.

44  The Court also determined that the 1976 Treaty on the Delimitation of Marine and Submarine Areas and Related Matters between the Republic of Panama and the Republic of Colombia was not relevant for the delimitation between the parties in the present case since it involved third states. Concerning the 1977 Treaty on Delimitation of Marine and Submarine Areas and Maritime Cooperation between the Republic of Colombia and the Republic of Costa Rica (not ratified by Costa Rica (2018 Judgment para. 57)), the Court found that there was no evidence that Costa Rica renounced its maritime entitlements with regard to a state other than Colombia.

45  Noting that Articles 74 and 83 UNCLOS required the Court to ‘achieve an equitable solution’ (2018 Judgment para. 135), the Court then applied its established methodology in three stages in order to define the single maritime boundary concerning the EEZ and the CS.

46  As a first step, the Court then proceeded to draw a provisional equidistance line. In this respect, the Court noted that the endpoint of the delimitation of the TS, point Lx as described in paragraph 106 of its judgment, constituted the starting point of the provisional equidistance line.

47  As regards the use of base points for the construction of the provisional equidistance line, Nicaragua placed base points on the Corn Islands and two ‘minor maritime features’ (2018 Judgment para. 141), Paxaro Bovo and Palmenta Cays. Costa Rica contested this placement. With respect to the Corn Islands, the Court concluded that base points should be placed on these features since they are fully entitled islands within the meaning of Article 121 UNCLOS and thus generate an EEZ and a CS (see also Rocks). These islands in fact are inhabited and sustain economic life. As regards Paxaro Bovo and Palmenta Cays, which are situated at 3 nm and 1 nm from Nicaragua’s mainland coast, the Court considered these features as being ‘assimilated to the coast’ (ibid. para. 142). Therefore, the Court concluded that it was appropriate to place base points on those features for the construction of the provisional equidistance line. As for the rest of the base points, the Court placed them on the natural coast and on solid land.

48  As a second step, the Court considered whether there existed relevant circumstances which justified an adjustment of the equidistance line. Observing the disproportionate impact that the Corn Islands would have on the provisional equidistance line, given their limited size and significant distance from the mainland coast (26 nm), the Court considered that these islands should be given half effect. The Court also observed that this produced a shifting of the equidistance line in favour of Costa Rica.

49  Since the resulting adjusted equidistance line of the EEZ and CS was considered complex, the Court decided to adopt a simplified line on the basis of the most significant turning points on the adjusted equidistance line. The simplified line is described in paragraph 158 of the Court’s judgment in the present joined cases as composed of the points Lx (endpoint of the delimitation of the TS) and points M to V with specific coordinates. The Court also noted that the delimitation line continued following a geodetic line starting at an azimuth of 77 49’ 08’’.

50  As a third step, the Court assessed whether there existed a marked disproportionality between the length of the parties’ relevant coasts and the maritime areas found to appertain to them (‘disproportionality test’). In this regard, the Court concluded that the maritime boundary divided the relevant area into 73,968 km2 for Nicaragua and 30,873 km2 for Costa Rica, resulting in a ratio of 1:2.4 in favour of Nicaragua. The Court then observed that a comparison to the ratio of coastal lengths, as determined in paragraph 114 of its judgment (also 1:2.4 in favour of Nicaragua), did not show any ‘marked disproportion’ (ibid. para. 165). Consequently, the Court found that the delimitation line of the EEZ and the CS between the parties in the Caribbean Sea followed the simplified line as described in paragraph 158 of its judgment.

(c)  Maritime Delimitation in the Pacific Ocean

51  The Court followed the same methodology used for the delimitation of the TS, the EEZ, and the CS in the Caribbean Sea.

(i)  Starting Point of the Maritime Delimitation

52  Noting that the parties in the present case had agreed on the starting point of the maritime boundary in the Pacific Ocean, the Court concluded that the delimitation line starts at the midpoint of the closing line of Salinas Bay, which is drawn between Punta Zacate, on Costa Rica’s territory, and Punta Arranca Barba, on Nicaragua’s territory.

(ii)  Delimitation of the Territorial Sea

53  In relation to the base points used to construct the provisional equidistance line, the Court noted that Costa Rica and Nicaragua selected the same points. The Court then stated that there was no reason to depart from the base points selected by the parties. Therefore, the Court placed base points on certain features in the vicinity of Punta Zacate, Punta Descartes, and Punta Blanca on the Costa Rican coast, and on certain features in the vicinity of Punta Arranca Barba, Punta La Flor, Frailes Rocks, and Punta Sucia on the Nicaraguan coast.

54  With regard to special circumstances, the Court determined that the Santa Elena Peninsula (belonging to Costa Rica) could not be considered a ‘minor coastal projection’ (2018 Judgment para. 174) that had a disproportionate effect on the delimitation line as proposed by Nicaragua. In the Court’s view, the Santa Elena Peninsula constitutes a large portion of Costa Rica’s coast in the area of delimitation of the TS and thus it is not a special circumstance within the meaning of Article 15 UNCLOS which would justify an adjustment of the provisional median line in the TS.

55  The Court then described the delimitation line in paragraph 175 of its judgment as the line connecting the starting point and the points A to K. The Court also noted that the boundary in the TS shall terminate at point Kx with specific coordinates.

(iii)  Delimitation of the Exclusive Economic Zone and the Continental Shelf

56  With regard to the relevant coasts, the Court determined that the entire Nicaraguan coast, from Punta Arranca Barba to Punta Cosigüina, generates potential maritime entitlements overlapping with projections from the coast of Costa Rica. The Court then concluded that the length of Nicaragua’s relevant coast measured along a straight line was 292.7 km long. As for Costa Rica’s relevant coast, the Court concluded that it ran along the straight lines connecting Punta Zacate, Punta Santa Elena, Cabo Velas, Punta Guiones, and Cabo Blanco as well as the straight lines connecting Punta Herradura, the Osa Peninsula, Punta Llorona, and Punta Salsipuedes. The Court then concluded that Costa Rica’s relevant coast measured 416.4 km long.

57  In relation to the relevant area, the Court concluded that the potential maritime entitlements generated by the northern and the southern parts of Costa Rica’s relevant coast overlap with those generated by the relevant coast of Nicaragua. However, the Court excluded the maritime area enclosed by a line joining Cabo Blanco to Punta Herradura since the coast on that area does not generate potential maritime entitlements overlapping with those generated by Nicaragua’s coast. The Court then concluded that the relevant area measured approximately 164,500 km2.

58  Regarding the base points selected by the parties for the construction of the provisional equidistance line, the Court was of the view that they were ‘appropriate’ (para. 188) for drawing this line.

59  The Court then described the provisional equidistance line in paragraph 188 of its judgment as the line resulting from joining the points Kx (endpoint of the delimitation of the TS) and the points 1 to 9. The Court also noted that from point 9 the line continued following the geodetic line starting at an azimuth of 245 38’ 27.4’’ until it reaches the 200-nautical-mile outer limit of the EEZ of the parties.

60  With regard to the question whether it is necessary to adjust the provisional equidistance line, the Court considered that the disproportionate effect on the direction of this line caused by placing a base point in the Santa Elena Peninsula (belonging to Costa Rica) produced a significant and inequitable cut-off effect of Nicaragua’s coastal projections. Therefore, the Court considered that in order to achieve an equitable solution the provisional equidistance line needed to be adjusted by giving half effect to the Santa Elena Peninsula.

61  Concerning the cut-off effect of the Nicoya Peninsula (belonging to Costa Rica) over Nicaragua’s coastal projections, the Court concluded that since the coast of this peninsula constitutes a sizeable portion of the coast of Costa Rica in the area to be delimited, it should be given no less than full effect. Therefore, the Court did not deem it necessary to adjust the provisional equidistance line because of the presence of the Nicoya Peninsula.

62  The Court then described the maritime boundary in the EEZ and the CS between the parties in the Pacific Ocean in paragraph 200 of its judgment as the line resulting from joining the point Kx (endpoint of the delimitation of the TS) and the points 1’ to 24’ as well as point 9 (as described for the provisional equidistance line). The Court also noted that from point 9 the adjusted line continued following the geodetic line starting at an azimuth of 245 38’ 27.4’’ until it reaches the 200-nautical-mile outer limit of the EEZ of the parties.

63  In view of the complexity of that line, the Court decided to adopt a simplified line as described in paragraph 201 of its judgment as the line resulting from joining the point Kx and the points L to S, noting also that the delimitation line continued following the geodetic line starting at an azimuth of 245 38’ 27.4’’ until it reaches the 200-nautical-mile line.

64  The Court then applied the ‘disproportionality test’ (2018 Judgment para. 202). In this respect the Court noted that the maritime boundary divided the relevant area into 71,500 km2 for Nicaragua and approximately 93,000 km2 for Costa Rica, resulting in a ratio of 1:1.30.4 in favour of Costa Rica. The Court then observed that a comparison to the ratio of coastal lengths, as determined in paragraph 180 of its judgment (1:1.42 also in Costa Rica’s favour), did not result in ‘gross disproportionality’ (ibid. para. 203). Consequently, the Court found that the delimitation line of the EEZ and the CS between the parties in the Pacific Ocean followed the simplified line as described in paragraph 201 of its judgment.

E.  Assessment

65  With respect to the methodology applied for the construction of a single maritime boundary delimiting the TS, EEZ, and CS between the parties, the Court adopted the ‘three stage methodology’ that it developed in Maritime Delimitation in the Black Sea (2009) (see also Black Sea). As mentioned above, this methodology consists of three steps: a) the drawing of a provisional median/equidistance line; b) the adjustment of that provisional line if there are special or relevant circumstances that justify such a shift; and c) the ‘disproportionality test’, to check whether there exists a marked disproportionality between the length of the parties’ relevant coasts and the maritime areas found to appertain to them.

66  This ‘three stage approach’ has not only been reiterated by the Court in its previous jurisprudence (e.g., Territorial and Maritime Dispute Case (Nicaragua v Colombia) (2012) and Maritime Dispute (Peru v Chile) (2014)), but it has also been followed by other international courts and tribunals dealing with maritime delimitation cases (Maritime Delimitation Cases before International Courts and Tribunals). For instance, in the cases concerning the Delimitation of the Maritime Boundary in the Bay of Bengal (Bangladesh/Myanmar) (2012) and the Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives) (2023), both heard by the International Tribunal for the Law of the Sea (ITLOS), and the Bay of Bengal Maritime Boundary Arbitration (Bangladesh and India) (2014), decided by an arbitral tribunal.

67  In relation to the starting point of the maritime boundary delimitation between the parties on the Caribbean Sea side, the Court applied the reasoning previously used by it in the case concerning the Territorial and Maritime Dispute in the Caribbean Sea (Nicaragua v Honduras) (2007) (Maritime Delimitation between Nicaragua and Honduras in the Caribbean Sea Case (Nicaragua v Honduras)). In the latter case, the Court had decided, in its 2007 judgment, to place the starting point of the maritime boundary 3 miles out to sea from the point that had already been identified in 1962 by a Mixed Commission at the mouth of the River Coco as described by the Court in its 2007 judgment (Mixed Commissions). The Court based its decision on the unstable nature of the relevant coasts in that area since the River Coco and the coastline north and south of it showed a very active morpho-dynamism resulting in the river mouth constantly changing its shape and forming unstable islands and shoals where the river deposits its sediment. This in turn made it impossible for the Court to identify viable and certain base points, points that would not become uncertain within a short period, for the construction of a provisional equidistance line.

68  Likewise, in the present case the great instability of the coastline in the area of the mouth of the San Juan River prevented the Court from identifying a suitable base point on the sandspit. Therefore, the Court opted for a fixed-point-at-sea solution connected to the starting point on the coast by a mobile line.

69  That solution had previously been adopted in other cases where there was an uncertain land boundary terminus, such as the Maritime Boundary between Guinea and Guinea-Bissau Arbitration (Guinea v Guinea-Bissau) (1985).

70  Concerning the fact that no effect was given to the sandbar separating the Harbor Head Lagoon from the Caribbean Sea in the maritime delimitation boundary, the Court did not expressly state that the reason why it did not give any effect to the sandbar was the non-encroachment or the cut-off effect that this ‘minor feature’ would produce. However, the Court seems to imply this idea when saying that the potential maritime entitlements that could be attributed to the sandbar could ‘break… the continuity of Costa Rica’s territorial sea’ (2018 Judgment para. 105). This implies that any potential adjacent maritime space to Nicaragua’s sandbar and its situation as an enclave on the Costa Rican coast would encroach or cut off Costa Rica’s coastal projections.

71  In the same vein, by referring to the sandbar as ‘a minor feature without vegetation and characterized by instability’ (2018 Judgment para. 89) whose potential entitlements, even if only a TS, would be of little use to Nicaragua, the Court seems to suggest two things: first, that this area could not provide suitable base points, and second, that because of those particular physical characteristics described by the Court, giving full or reduced effect to this feature could lead to the achievement of an inequitable result. In this sense, the Court has previously deprived of any effect small or irregular coastal features because of their distorting effect over the provisional equidistance line. For example, in the case concerning the Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v Bahrain), the Court decided to disregard Qit’at Jaradah (belonging to Bahrain), a small feature considered by the Court as a ‘tiny island’, ‘uninhabited and without any vegetation’ (Merits (2001) para. 219), because of its disproportionate effect on the delimitation line. This approach is also in line with modern delimitation jurisprudence. See also, more recently, the case concerning the Maritime Delimitation in the Indian Ocean (Somalia v Kenya), where the ICJ considered that it was not appropriate to place base points either on the ‘tiny arid Diua Damasciaca islets’ or on the low-tide elevation off Ras Kaambooni, which is ‘a minor protuberance in Somalia’s otherwise relatively straight coastline’, because it ‘would have a disproportionate impact on the course of the median line in comparison to the size of these features’ (Judgment (2021) para. 114; Low-Tide Elevations).

Further Bibliography

  • S Fietta, and R Cleverly, A Practitioner’s Guide to Maritime Boundary Delimitation (OUP 2016).

  • G Guez, ‘International Court of Justice: Maritime Delimitation in the Caribbean Sea and the Pacific Ocean (Costa Rica v Nicaragua) and Land Boundary in the Northern Part of Isla Portillos (Costa Rica v Nicaragua)’ (2018) 33 IJMCL 827–35.

  • E Sobenes Obregon and B Samson (eds), Nicaragua before the International Court of Justice: Impacts on International Law (Springer 2018).

  • C Lathrop, ‘Costa Rica-Nicaragua [Report Number 2-34]’ in C Lathrop (ed.), International Maritime Boundaries Online (Brill-Nijhoff 2020) <https://referenceworks.brill.com/display/db/mboo> (accessed 31 January 2025).

  • N Klein and K Parlett, Judging the Law of the Sea: Judicial Contributions to the UN Convention on the Law of the Sea (OUP 2022).

  • A Horna, Law of the Sea and Maritime Delimitation: State Practice and Case Law in Latin America and the Caribbean (Routledge 2023).

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