Crimean Coastal State Rights and the Resilience of International Arbitration

Introduction

On 15 June 2026, the Permanent Court of Arbitration published its merits award in Ukraine v. the Russian Federation concerning coastal state rights in the Black Sea, Sea of Azov, and Kerch Strait (PCA Case No. 2017-06). The award itself had been issued on 22 April 2026. The case concerned an array of claims by Ukraine relating to navigation, the maritime environment, and underwater cultural heritage; it also engaged questions on the legal status of waters surrounding the Crimean Peninsula. It was found that Russia had violated its obligations under the United Nations Convention on the Law of the Sea (UNCLOS) in relation to environmental impact assessments and the duty to cooperate with respect to the marine environment. However, the arbitral tribunal constituted under UNCLOS rejected Ukraine’s claims on navigation, underwater cultural heritage, and aggravation of the dispute, and declined to award reparations or other remedies including the ordering of cessation, assurances, and guarantees of non-repetition.

Much of the initial reporting characterised the outcome as a defeat for Ukraine, with the Tribunal declining to award any reparation at all, holding that declaratory relief was sufficient in respect of the breaches it had found. Yet the picture is more nuanced: the Tribunal not only upheld jurisdiction, but also found Russia in breach of three categories of environmental obligation under UNCLOS. Further, and beyond its doctrinal significance, the case is a remarkable illustration of the capacity of international arbitration to function during war. Both parties participated fully in the proceedings despite being engaged in the largest armed conflict in Europe since 1945.

In 2020, the preliminary objections award was analysed on this blog. This post examines the merits award, its implications, and what the process tells us about the role of international arbitration as a mechanism for managing disputes even where broader political relations have entirely broken down.

Procedural history

The case was originally initiated by Ukraine in September 2016 and proceeded through two rounds of written pleadings to a merits hearing held at the Peace Palace from 23 September to 5 October 2024. The five-member Tribunal was chaired by Judge Jin-Hyun Paik (Republic of Korea), with Judges Bouguetaia (Algeria) and Gómez-Robledo (Mexico) appointed under Article 3(d) of Annex VII UNCLOS. The Tribunal was rounded out by Professor Vaughan Lowe KC (United Kingdom), appointed by Ukraine, and Professor Alexander Vylegzhanin (Russian Federation), appointed by the Russian Federation (replacing Judge Golitsyn following his death in March 2023).

The Tribunal rendered a preliminary objections award on 21 February 2020. That award addressed two fundamental challenges to the Tribunal’s jurisdiction. First, Russia argued that Ukraine’s claims necessarily implicated sovereignty over Crimea, a dispute over which the Tribunal lacked jurisdiction. The Tribunal accepted that a sovereignty dispute existed and could not simply be disregarded but concluded that it could exercise jurisdiction over claims that did not require determination of sovereignty as an ancillary matter, while excluding those that did. Second, Russia contended that the Sea of Azov and Kerch Strait constituted shared internal waters governed by the bilateral Azov/Kerch Treaty rather than UNCLOS, such that the Tribunal lacked ratione materiae jurisdiction entirely. The Tribunal characterised this objection as not “exclusively preliminary” and reserved it for the merits phase.

Jurisdictional objections at the merits stage

At the merits hearing, Russia advanced three general objections to jurisdiction that had not been disposed of in 2020. All three were rejected unanimously.

First, Russia invoked Article 298(1)(a)(i) of UNCLOS, arguing that Ukraine’s claims concerned historic bays or titles over which Russia had made an optional exception to compulsory dispute settlement. The Tribunal rejected this characterisation of the claims. Second, Russia renewed its argument (related to, but distinct from, its 2020 Sea of Azov objection) that the relevant waters constituted internal waters falling entirely outside the regulatory scope of UNCLOS. The Tribunal accepted that certain waters retained their pre-existing status as internal waters but held that specific Ukrainian claims could nonetheless concern the interpretation or application of UNCLOS even if the waters in question were internal waters and thus remained justiciable. Third, Russia argued that a fundamental change of circumstances following the September 2022 annexations deprived the Tribunal of jurisdiction. The Tribunal held, consistently with established authority, that jurisdiction is to be assessed at the date of institution of proceedings (16 September 2016), and that subsequent events could not retroactively divest it of competence.

With these objections dismissed, the Tribunal proceeded to the substance of Ukraine’s claims.

Navigation

Ukraine’s most ambitious claims concerned navigation in the Kerch Strait and Sea of Azov. These claims sought to characterise the Kerch Strait as a strait used for international navigation within the meaning of Article 37 UNCLOS. Had this succeeded, it would have entitled all vessels to a right of transit passage through the Strait (effectively internationalising a waterway that Russia controlled, and which the Tribunal found led only to internal waters). 

Article 37 of UNCLOS applies to “straits used for international navigation” that connect “one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone.” The Kerch Strait connects the Black Sea (where coastal states have EEZs) to the Sea of Azov. Because the Tribunal found (on the basis of the 2003 bilateral treaty and historic practice) that the Sea of Azov constitutes internal waters shared between Ukraine and Russia, the geographic criterion of Article 37 was not met: the Strait connects an EEZ to internal waters, not to another area of high seas or EEZ. However, interestingly, the Tribunal observed that the bilateral Azov/Kerch Treaty did establish navigational rights that Russia may have breached. But because Ukraine had pleaded its case exclusively under UNCLOS, the Tribunal could not examine these claims without exceeding its mandate. The principle of ne ultra petita prevented the Tribunal from adjudicating on a legal basis not advanced by the claimant.

This outcome demonstrates that the framing of claims matters and represents a practical lesson for States contemplating UNCLOS arbitration. A Tribunal constituted under Annex VII is constrained by the legal bases pleaded. Broader treaty rights cannot be vindicated if not properly put in issue, no matter their merit.

The Tribunal also addressed Ukraine’s remaining navigation sub-claims. First, Ukraine alleged that Russia’s six-month closure of areas of the Black Sea violated the right of innocent passage; the Tribunal upheld the closure as a lawful exercise of Russia’s power under Article 25(3) to suspend innocent passage temporarily and without discrimination for the protection of its security. Second, Ukraine claimed that Russia impeded navigation in the Sea of Azov; this was rejected on the basis that the relevant UNCLOS provisions invoked by Ukraine were inapplicable, given the Tribunal’s finding that the Sea of Azov constituted the internal waters of both parties at the time the case was initiated. Third, Ukraine alleged that Russia unlawfully seized and reflagged Ukrainian jack-up drilling rigs; the Tribunal found it lacked jurisdiction over the seizure claim and dismissed the reflagging claim on the merits, holding that Article 91 had not been violated.

Marine environmental protection

It was on environmental claims that Ukraine achieved its most significant success. The Tribunal found that Russia had violated three distinct categories of obligation.

First, Russia breached Article 206 by conducting inadequate environmental impact assessments for the Kerch Strait Bridge, subsea power cables, and gas pipeline: the EIAs were deficient in both their temporal scope and baseline data. Second, Russia violated Articles 205 and 206 by failing to communicate the results of those assessments to competent international organisations. Third, and importantly, the Tribunal found that Russia did not violate Articles 204 or 205 with respect to ongoing monitoring and publication of pollution monitoring results, holding that Ukraine had not adduced clear evidence of a breach in this regard. However, the combination of the Article 206 assessment failures and the Article 205 communication failures grounded a further finding that Russia breached its duties of cooperation under Articles 123, 192, and 194; obligations that require Black Sea littoral States to coordinate on environmental protection.

Finally, Ukraine’s claim regarding an oil spill near Sevastopol was dismissed in its entirety: the Tribunal held the incident was de minimis and did not give rise to violations of the relevant UNCLOS provisions.

The Tribunal’s treatment of the duty to cooperate is noteworthy for its express statement that these obligations persist “even in times of tension and hostility”; a formulation that implicitly addresses, without resolving, the broader question of how peacetime environmental treaty obligations interact with the lex specialis of the laws of armed conflict.

Underwater cultural heritage (UCH)

Ukraine’s UCH claims were dismissed in their entirety. The Tribunal confirmed that Article 303(1) imposes a due diligence obligation on States to protect objects of an archaeological and historical nature found at sea, and that the 2001 UNESCO Convention on the Protection of the Underwater Cultural Heritage and its annexed Rules inform the content of that duty without importing binding obligations into UNCLOS. On the facts, Ukraine identified four specific incidents of alleged damage to UCH sites: (1) damage to a Byzantine-era shipwreck; (2) the removal of a terracotta sculpture fragment; (3) interference with a submerged Kittyhawk aircraft; and (4) interference with a submerged Airacobra aircraft. In each case, the Tribunal found the evidence insufficient to establish a breach.

The Tribunal also rejected Russia’s invocation of the clean hands doctrine as a bar to Ukraine’s claims, holding that the doctrine does not operate as a general admissibility defence under UNCLOS.

Aggravation

Ukraine’s final claim, that Russia had aggravated or extended the dispute during proceedings, was likewise dismissed. The Tribunal acknowledged that a duty not to aggravate a pending dispute exists as an aspect of the obligations of good faith and peaceful settlement under Articles 279 and 300.

The Tribunal adopted the three-limb test for aggravation articulated in the South China Sea arbitration: a party may aggravate a dispute by (i) continuing actions alleged to violate the other’s rights so as to render the violation more serious; (ii) taking actions that would frustrate the effectiveness of a potential decision or render its implementation significantly more difficult; or (iii) undermining the integrity of the proceedings themselves, including by rendering the Tribunal’s work significantly more onerous or decreasing the likelihood of the proceedings leading to resolution. Applying this test, the Tribunal found that Ukraine had not demonstrated that any of Russia’s conduct crossed the aggravation threshold, a high bar that requires something beyond the continuation of the underlying dispute.

Relief, enforcement and competing narratives

In respect of its successful environmental claims, Ukraine sought reparation in the form of a declaration of wrongfulness together with additional remedial measures. However, the Tribunal held that the declaration of Russia’s breaches of Articles 123, 192, 194, 205, and 206 of UNCLOS was itself a sufficient and appropriate remedy in the circumstances. It therefore declined to order reparations, cessation, or guarantees of non-repetition.

This outcome immediately generated competing narratives. Ukraine emphasised the Tribunal’s findings of Russian violations of international law, framing the award as juridical vindication of its coastal State rights. Russia emphasised the dismissal of Ukraine’s navigation and reparations claims, and particularly the denial of the specific remedies sought.

The real question is not one of enforcement (given declaratory relief requires no execution mechanism), but rather whether the Tribunal’s authoritative findings will exert any normative pressure on Russia’s future conduct. How this plays out in practice remains to be seen, but regardless of this, to dismiss the award as merely symbolic would be to misunderstand the function of international adjudication. Declaratory relief crystallises legal obligations; it establishes an authoritative record; and it creates a juridical baseline against which future conduct (and potentially future negotiations) will be assessed. The award’s practical significance may yet depend on broader developments.

Conclusion: Arbitration as peace infrastructure

In the author’s assessment, neither side’s characterisation withstands scrutiny (which is unsurprising, given the highly politicised context). Russia cannot credibly claim decisive victory when the Tribunal found it in breach of UNCLOS environmental obligations (findings that contribute to the broader corpus of legal determinations of Russian wrongfulness). Equally, Ukraine’s framing of the award as a vindication elides the fact that it was denied reparations and failed on the majority of its substantive claims, including all its UCH claims. The more accurate characterisation is that the award represents a qualified procedural success for Ukraine (in the sense that the process worked, jurisdiction was upheld, and breaches were found) but a substantive disappointment in terms of the relief obtained.

Regardless of the outcome, these proceedings represent a good demonstration of the capacity of international arbitration to function under conditions of armed conflict. Russia’s choice to participate (even as it boycotted parallel proceedings before the International Court of Justice relating to the legality of its invasion) is consistent with what has been identified as a broader strategic shift. Having initially disengaged from most international proceedings following 2022, Russia has progressively returned to active procedural participation across fora, apparently concluding that engagement enables it to influence the pace, scope, and framing of disputes more effectively than absence. That preference, whatever its motivation, is itself significant. It demonstrates that even between States engaged in armed conflict, international arbitration can absorb a defined technical dispute into predictable, rules-based channels; produce binding determinations that both parties treat as procedurally legitimate; and establish a juridical baseline that any future peace settlement will need to address.

This is the case for arbitration as peace infrastructure. Not necessarily as a mechanism that resolves armed conflicts, but as one that survives them. It preserves a framework of legal engagement, a common procedural language, and a set of institutional habits that may, in time, contribute to the reconstruction of a broader normative order.