On 22 April 2026, an Annex VII arbitral tribunal issued its Award in Ukraine v. Russian Federation, a major law-of-the-sea arbitration concerning coastal State rights in the Black Sea, the Sea of Azov, and the Kerch Strait. The arbitration was brought under the United Nations Convention on the Law of the Sea (“UNCLOS”), with the Permanent Court of Arbitration (“PCA”) acting as registry.[1]
The Award is a mixed result. Ukraine succeeded on important environmental claims: the Tribunal held that the Russian Federation violated UNCLOS by conducting environmental impact assessments (“EIAs”) for the Kerch Strait bridge, power cables, and gas pipelines in a manner inconsistent with Article 206, by failing to publish or communicate the EIA reports consistently with Articles 205 and 206, and by failing to cooperate with respect to protection and preservation of the marine environment under Articles 123, 192, and 194.[2] Ukraine lost most of its other claims, including claims based on transit passage, navigation in the Sea of Azov, reflagging of jack-up drilling rigs (“JDRs”), underwater cultural heritage (“UCH”), and alleged aggravation of the dispute.[3]
The decision matters because it clarifies three points of broader significance. First, an Article 298 declaration excluding disputes involving historic bays or titles is not self-judging: a tribunal may decide whether the waters are in fact a historic bay or subject to historic title.[4] Second, the Tribunal found that the Sea of Azov and the Kerch Strait retained the status of internal waters after the dissolution of the Soviet Union, but that this did not automatically remove all UNCLOS issues from the Tribunal’s jurisdiction.[5] Third, the Tribunal treated environmental cooperation duties as continuing even in times of tension and hostility.[6]
Facts
Ukraine and the Russian Federation are both parties to UNCLOS. Ukraine ratified UNCLOS on 26 July 1999, and the Russian Federation ratified it on 12 March 1997.[7]
The dispute concerned events after 2014 in the Black Sea, the Sea of Azov, and the Kerch Strait. Ukraine alleged that the Russian Federation violated UNCLOS by interfering with navigation and transit passage, jeopardising the marine environment, mistreating UCH, and aggravating the dispute after the arbitration began.[8]
The legally material conduct fell into four categories. First, Ukraine challenged the Kerch Strait bridge and related measures, arguing that they restricted navigation through the Kerch Strait and to Ukrainian ports in the Sea of Azov.[9] Second, Ukraine challenged the alleged seizure and reflagging of two Ukrainian-flagged JDRs.[10] Third, Ukraine argued that construction works in the Kerch Strait were carried out without adequate EIAs, monitoring, reporting, and cooperation, and that the Russian Federation failed to notify or cooperate with Ukraine concerning a 2016 oil spill near Sevastopol.[11] Fourth, Ukraine claimed that the Russian Federation failed to protect UCH and aggravated the dispute during the arbitration.[12]
The Russian Federation raised threshold objections. It argued that the Sea of Azov and the Kerch Strait were internal waters because they formed part of a historic bay or were subject to historic title, and that both States’ Article 298 declarations excluded disputes involving historic bays or titles from compulsory UNCLOS dispute settlement.[13] In the alternative, it argued that UNCLOS did not regulate the relevant conduct because the Sea of Azov and the Kerch Strait were internal waters.[14] It also argued that later territorial developments meant that Ukraine no longer qualified as a coastal State in relation to the Sea of Azov and that the claims implicated sovereignty disputes beyond the Tribunal’s jurisdiction.[15]
Before the final Award, the Tribunal had already held in its preliminary-objections phase that it lacked jurisdiction over Ukraine’s claims to the extent that deciding them would require a ruling, directly or implicitly, on sovereignty over Crimea. It reserved for the merits the Russian Federation’s objection concerning activities in the Sea of Azov and the Kerch Strait.[16]
Issues
The Tribunal faced five core legal questions.
First, did the parties’ Article 298 declarations deprive the Tribunal of jurisdiction because the dispute involved historic bays or historic titles?[17]
Second, did the Sea of Azov and the Kerch Strait retain internal-waters status after the dissolution of the Soviet Union, and, if so, did that status bar Ukraine’s UNCLOS claims?[18]
Third, did the Russian Federation violate UNCLOS navigation rules by constructing the Kerch Strait bridge, allegedly restricting passage, stopping or inspecting vessels, closing the southern entrance to the Kerch Strait, or reflagging the JDRs?[19]
Fourth, did the Russian Federation violate UNCLOS environmental obligations by failing to conduct adequate EIAs, publish or communicate their results, monitor environmental impacts, cooperate with Ukraine, or respond properly to the Sevastopol oil spill?[20]
Fifth, did the Russian Federation violate Article 303 on UCH or Articles 279 and 300 by aggravating the dispute?[21]
Ruling
The Tribunal held that an Article 298 historic-bay or historic-title objection requires an objective assessment. A dispute does not become one involving historic bays or historic titles merely because one party asserts historic title.[22] The Tribunal therefore could determine whether the Sea of Azov and the Kerch Strait were a historic bay or subject to historic title. It found that they were not internal waters subject to historic title and rejected the Russian Federation’s first general objection.[23]
The Tribunal nevertheless held that the internal-waters status of the Sea of Azov and the Kerch Strait continued after the dissolution of the Soviet Union.[24] That finding defeated Ukraine’s transit-passage claims because the Kerch Strait did not qualify as a strait used for international navigation under Article 37, which requires a strait connecting one part of the high seas or an exclusive economic zone with another part of the high seas or an exclusive economic zone. Transit passage under Articles 38, 43, and 44 therefore did not apply.[25]
The Tribunal held, however, that navigation in internal waters can still fall within the scope of UNCLOS for jurisdictional purposes. The Convention recognises coastal-State authority over internal waters, and the existence of only limited express provisions on internal waters did not mean that navigation there was wholly outside UNCLOS.[26] The Tribunal therefore rejected the Russian Federation’s broad jurisdictional objection but dismissed Ukraine’s specific navigation claims on the merits or because the invoked provisions were inapplicable.[27]
On the environmental claims, Ukraine won in part. The Tribunal held that the Russian Federation’s EIAs for the Kerch Strait bridge, power cables, and gas pipelines were inconsistent with Article 206; that the Russian Federation failed to meet Article 205 requirements for communicating reports of EIA results; and that, through those failures and a failure to cooperate, the Russian Federation did not fulfil Articles 123, 192, and 194. The Tribunal rejected Ukraine’s environmental claims concerning the fibre-optic cable, monitoring and monitoring reports, and the Sevastopol oil spill.[28]
On UCH, Article 303(1) provides that States must protect objects of an archaeological and historical nature found at sea and cooperate for that purpose.[29] The Tribunal treated this as a due-diligence obligation, meaning an obligation of conduct rather than a guarantee of result. It held that Ukraine had not proved a violation concerning the Byzantine ship, the Terracotta sculpture head fragment, or the Kitty Hawk and Airacobra aircraft.[30]
The Tribunal rejected all remaining claims, including the navigation, JDR, UCH, oil-spill, monitoring, and aggravation claims.[31] It granted declaratory relief only for the environmental violations and declined to order cessation, assurances and guarantees of non-repetition, reparation, amendment of the Rules of Procedure, or costs-shifting.[32]
Reasoning and Disposition
The Tribunal’s reasoning began with jurisdiction. The Russian Federation’s first objection depended on the argument that the Sea of Azov and the Kerch Strait were a historic bay or subject to historic title, and that the parties’ Article 298 declarations therefore removed the dispute from compulsory UNCLOS adjudication.[33] The Tribunal rejected the premise. It reasoned that Article 298’s reference to disputes “involving” historic bays or titles assumes the existence of such bays or titles and a party cannot defeat jurisdiction by merely asserting them.[34] The Tribunal then found no historic title: the Azov/Kerch Cooperation Treaty did not establish that the waters were historic in that legal sense, the 1957 UN Memorandum and scholarly materials were not sufficiently weighty, and Ukraine’s Article 298 declaration was not an implicit recognition of Russian historic title.[35]
The second jurisdictional issue was more nuanced. The Tribunal accepted that the Sea of Azov and the Kerch Strait continued to be internal waters after the Soviet Union dissolved.[36] However, it rejected the Russian Federation’s broader argument that this status removed all navigation claims from the Convention. UNCLOS provisions on coastal-State sovereignty, admission of foreign vessels, and limits on internal-waters authority were enough to support jurisdiction over at least some disputes concerning navigation in internal waters.[37] The important distinction was between jurisdiction and applicable substantive rules: the Tribunal could have jurisdiction, while still concluding that particular provisions invoked by Ukraine did not apply.[38]
That distinction shaped the navigation outcome. Ukraine’s strongest navigation theory depended on the Kerch Strait being a strait used for international navigation, which would trigger the transit-passage regime in Articles 38, 43, and 44.[39] The Tribunal rejected that theory because, in light of the internal-waters status of the Sea of Azov and the Kerch Strait, the Kerch Strait did not connect one part of the high seas or an exclusive economic zone with another. The transit-passage provisions were therefore inapplicable.[40]
The Tribunal also rejected Ukraine’s claim concerning closure of the southern entrance to the Kerch Strait in portions of the Black Sea. It accepted that Article 25(3) allows a coastal State temporarily to suspend innocent passage where the suspension is essential for its security and is duly published and non-discriminatory among foreign ships.[41] It found no violation because the Russian Federation’s measure applied equally to foreign warships and governmental vessels of different nationalities, was connected to security concerns, and was publicised through Notices to Mariners.[42]
For the Sea of Azov inspections and navigation claims, the same internal-waters reasoning was decisive. Articles 2, 58, 87, and 92 were inapplicable to Ukraine’s claims concerning alleged impediments to navigation in the Sea of Azov.[43] On the JDRs, the Tribunal held that it lacked jurisdiction to decide the release of the rigs, and that the Russian Federation did not violate Article 91 by reflagging them.[44]
The environmental claims came out differently because Part XII of UNCLOS supplied applicable obligations. Ukraine alleged that the Russian Federation failed to assess, monitor, publish, report, cooperate, and protect the marine environment in connection with the Kerch Strait construction projects and the Sevastopol oil spill.[45] The Tribunal accepted part of that case. It held that Russia’s EIAs for the bridge, power cables, and gas pipelines were not consistent with Article 206. It also held that Russia failed to fulfil Article 205 requirements to communicate reports of the EIA results. Those failures, together with Russia’s failure to cooperate for protection and preservation of the marine environment in and around the Kerch Strait, also breached Articles 123, 192, and 194.[46]
The Tribunal did not accept all of Ukraine’s environmental theories. It held that the Russian Federation’s decision not to conduct an EIA for the fibre-optic cable did not violate Article 206. It also held that the evidence did not establish a breach of Articles 204 and 205 concerning monitoring and monitoring reports. Finally, it rejected the claim that the Russian Federation’s response to the Sevastopol oil spill violated Articles 123, 192, 194, 198, 199, 204, or 205.[47]
The UCH claim failed because Article 303(1) is an obligation of conduct. The Tribunal accepted that States have an affirmative duty to protect objects of archaeological and historical nature found at sea and to cooperate for that purpose. But Ukraine still had to prove that Russia’s conduct fell below the required standard. The Tribunal found that it had not done so for the four excavations at issue. [48]
The aggravation claim also failed. Ukraine argued that Russia aggravated and extended the dispute after the arbitration began, invoking Articles 279 and 300.[49] The Tribunal ultimately rejected the claim along with all claims other than the specified environmental violations.[50]
The disposition was declaratory. The Tribunal declared Russia in breach only as to the environmental violations identified in the dispositif.[51] It considered those declarations appropriate relief and held that it was unnecessary to order cessation, assurances and guarantees of non-repetition, or reparation.[52] It also declined to amend the Rules of Procedure to extend the time for interpretation or implementation requests from six months to 24 months.[53] Each party was ordered to bear its own costs.[54]
Conclusion
The Award is relevant less because of the number of claims Ukraine won, and more because of the doctrinal lines it draws. Ukraine obtained significant declarations that Russia breached UNCLOS environmental obligations in relation to Kerch Strait construction projects. Those declarations reinforce the practical importance of EIAs, publication and communication of EIA results, and cooperation over shared marine environments.[55]
At the same time, the Award shows the limits of UNCLOS navigation claims where the disputed waters are treated as internal waters. The Tribunal rejected a self-judging approach to historic-title objections, but it also accepted that the Sea of Azov and the Kerch Strait retained internal-waters status after the Soviet Union’s dissolution. That finding largely defeated Ukraine’s transit-passage and Sea of Azov navigation claims.[56]
For future disputes, the most important lesson is that jurisdiction, status, and merits must be kept separate. A tribunal may have jurisdiction to decide whether UNCLOS applies, yet still conclude that the specific substantive provisions invoked by the claimant do not apply. Conversely, even where navigation claims fail, environmental duties may remain enforceable. The Award therefore stands as a careful but consequential decision on the intersection of internal waters, historic-title objections, and environmental due diligence under UNCLOS.
[1] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1- 2.
[2] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1281 (5)-(7).
[3] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 726, 1152, 1234.
[4] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 295-299, 301.
[5] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 239, 337, 358, 402 404.
[6] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 960.
[7] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 1.
[8] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 2, 4-8.
[9] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 5, 101 (a)-(c).
[10] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 5, 101 (d).
[11] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 6, 32.
[12] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 7-8.
[13] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 9, 113, 117.
[14] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 113.
[15] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 10, 113.
[16] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 12, 38.
[17] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 301, 332.
[18] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 358, 393, 402, 404, 406.
[19] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 726 (a)-(d).
[20]Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 909, 974- 975.
[21] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1135, 1141, 1147, 1234.
[22] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 295-296.
[23] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 301, 332, 419.
[24] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 358, 361.
[25] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 425, 650, 652, 673.
[26]Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 621-623.
[27] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 406, 726 (a)-(c).
[28] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 975.
[29] United Nations Convention on the Law of the Sea, opened for signature 10 December 1982, Art. 303(1).
[30] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1106, 1135, 1141, 1152.
[31] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 726, 975, 1152, 1234.
[32] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1281 (9)-(11), 1267, 1270.
[33] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 9, 113, 117.
[34] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 294-296.
[35] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 326, 327, 323.
[36] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 358, 361, 393.
[37] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 621-624, 406.
[38] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 622, 651-652.
[39] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 101 (a), 425, 652.
[40] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 650-652, 726(a).
[41] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 674, 678-679, 680-684, 726(b).
[42] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 679-684.
[43] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 605-607, 693, 696, 726(c).
[44] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 705, 726 (d), 913.
[45] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 727-730.
[46] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 975.
[47] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 975.
[48] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 892, 1106, 1120, 1135, 1141, 1151-1152.
[49] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 8, 1153.
[50] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 975, 1234, 1281 (5)-(8).
[51] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 909, 975 (b)-(e), 1281 (5)-(7).
[52] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 1281(9)-(10).
[53] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 1281(11).
[54] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶ 1281(12).
[55] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 975(b)-(e), 1281(5)-(7).
[56] Ukraine v. Russian Federation, PCA Case No. 2017-06, UNCLOS, Award, 22 April 2026, ¶¶ 419(a)-(b), 650-652, 726 (a), (c).