2.2 The high seas in UNCLOS
As set out in the introduction of this thesis, UNCLOS defines the high seas as “all parts of the sea that are not included in the exclusive economic zone, in the territorial sea or in the internal waters of a State, or in the archipelagic waters of an archipelagic State”(1)Article 86(1) UNCLOS. Activities in the ABNJ are governed by Part VII of UNCLOS. Declaring the fundamental principle of the freedom of the high seas, Article 87 occupies a central place within UNCLOS. It affirms that the high seas are open to all States, a principle further reinforced by Article 89, which establishes that no State can subject any part of the high seas to its sovereignty. The high seas have been referred to as having “a somewhat anomalous status in an international system based on territorial States”(2)Douglas Guilfoyle, ‘The Oxford Handbook of the Law of the Sea’ (2016) Oxford Handbooks, chapter 10, page 204. Because no State may claim sovereignty over the high seas, they sit uneasily within an international legal system otherwise structured around territorial control. Guilfoyle further explains that this absence of sovereignty can be viewed either positively, as creating a shared global space governed collectively by international law, or negatively, giving the impression of regulatory gaps even though legal obligations exist and operate through different, non-territorial mechanisms such as flag State jurisdiction and due diligence(3)Ibid n49. Guilfoyle ultimately argues that the ABNJ is not “an unregulated legal vacuum(4)Ibid n49”, illustrating that environmental protection in these areas is primarily pursued through existing legal mechanisms, including procedural obligations such as EIAs, which are given effect through the exercise of flag State jurisdiction.
The freedoms that Article 87 sets out are the cornerstone of the open access to international waters that allows all States to conduct maritime activities uninterrupted. The wording “inter alia” from Article 87(1) indicates that the provision does not provide an exhaustive list of freedoms. At the same time, the second sentence makes it clear that the freedoms are exercised under the conditions laid down by UNCLOS and other rules of international law. The freedoms of the high seas are to be exercised in accordance with Article 87(2), which requires “due regard for the interests of other States in their exercise of the freedom of the high seas, and also with due regard for the rights under this Convention with respect to activities”(5)Article 87(2) UNCLOS in the high seas. The interpretation of the general duty of “due regard” will not be discussed further during this thesis, but the wording reflects the general and open‑textured language found in several of UNCLOS’ provisions. It has been argued that this open‑textured language in UNCLOS is partly a reflection of the “scope, procedure and complexity of the negotiations”(6)Julia Gaunce, ‘On the Interpretation of the General Duty of ‘Due Regard’’ (March 2017) Ocean Yearbook 32, (Leiden, Brill Nijhoff, 2018), page 1 that ultimately led to the adoption of UNCLOS(7)Ibid n53. The reference to due regard is used here to illustrate how UNCLOS frames high seas freedoms as qualified and relational, an approach that later finds more concrete expression in UNCLOS’ environmental due diligence obligations.
The freedom of the high seas, most importantly for the purposes of this thesis, includes the freedom of navigation on the high seas for all States(8)Article 87(1)(a) UNCLOS. Ships are permitted to travel through international waters, enabling global trade. The main rule on the high seas is that of flag State jurisdiction, entailing that a State Party does not have the right to enforce their national legislation on ships flying under the flag of another State(9)Article 91(1) UNCLOS.
It has been argued that Article 87(2) of UNCLOS, when read together with the environmental protection obligations set out in Part XII, conditions the exercise of high seas freedoms by requiring States to have due regard for their obligations to protect and preserve the marine environment(10)Alla Pozdnakova, ‘The High Seas Treaty and Shipping’ (2023), 570 MarIus, page 32. In this way, and in accordance with Article 194(2), State Parties must ensure that activities under their control or jurisdiction do not cause pollution spreading beyond areas of which that State exercises sovereign rights(11)Article 194(2) UNCLOS. On this view, a link is emerging between Article 87 and Article 194 in the balancing of the freedoms enjoyed by States on the high seas and their responsibilities to protect the marine environment. States are granted freedoms enabling activities on the high seas under Article 87, but the due diligence obligation from Article 194 requires that those activities are conducted with due regard for the protection of the marine environment. This balance is important, as it allows for the use of the high seas while ensuring that activities do not compromise the marine environment. This understanding was reaffirmed by ITLOS in its 2024 Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (‘COSIS Advisory opinion’)(12)Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (COSIS) (ITLOS Advisory Opinion, 21 May 2024) (Case No 31), https://www.itlos.org/cases/list-of-cases/case-no-31/ accessed 10.05.2026, in which ITLOS affirmed that the general obligation to protect and preserve the marine environment under Article 192 UNCLOS has a broad scope (13)Ibid n59, paragraph 385 .
Article 94 of UNCLOS concerns the jurisdiction of flag States and says that flag States are obliged to ensure that vessels under their flag comply with international regulations such as for the maintenance of vessels, maritime safety, and environmental protection. Flag States must both adopt and enforce regulations aligning with the international standards for maritime safety and environmental protection, such as measures to prevent pollution from ships and ensuring the proper maintenance and operation of ships. To achieve this, the flag State is required to “assume jurisdiction under its internal law over each ship flying its flag and its master, officers and crew in respect of administrative, technical and social matters concerning the ship”(14)Article 94(2)(b) UNCLOS, and Article 94(2)(a) further explains that exercising jurisdiction and control specifically includes that the flag States maintain a register of ships flying their flag.
For the purposes of this thesis, the above entails that flag States are to exercise due diligence through regulation and enforcement to secure compliance by vessels sailing under their flag with relevant pollution and environmental protection rules(15)Article 94 UNCLOS. In practical terms, this requires the flag State to exercise due diligence in its regulation of vessel-source pollution in accordance with Article 211 of UNCLOS, and, where relevant, conducting assessment of potential impacts under Article 206 for activities under its jurisdiction or control. Article 206 says that:
“When States have reasonable grounds for believing that planned activities under their jurisdiction or control may cause substantial pollution of or significant and harmful changes to the marine environment, they shall, as far as practicable, assess the potential effects of such activities on the marine environment and shall communicate reports of the results of such assessments in the manner provided in article 205.”(16)Article 206 UNCLOS
The article has several qualifications, that perhaps have played a part in the limited prominence of EIAs for shipping activities seen so far. The first part of Article 206 contains the wording “reasonable grounds for believing”(17)Article 206 UNCLOS, indicating an objective standard for the determination of this part of the threshold triggering the requirement of an EIA. The Tribunal in the COSIS Advisory Opinion noted that “the arbitral tribunal in the South China Sea Arbitration observed that the “terms ‘reasonable’ and ‘as far as practicable’ contain an element of discretion for the State concerned”(18)Ibid n59, paragraph 361, but concludes that the precautionary approach restricts the discretion as the State Party must make an objective determination of whether the activity under its jurisdiction or control “may cause substantial pollution of or significant and harmful changes to the marine environment”(19)Ibid n59, paragraph 361.
The next qualification to trigger the obligation to conduct an EIA under Article 206 is that the planned activity must be under the State Party’s “jurisdiction or control”(20)Article 206 UNCLOS. The Tribunal in the COSIS Advisory Opinion pointed out that the concept of jurisdiction or control is broad and that it, among other scenarios, may also encompass activities carried out in areas in which a State can exercise its competence or authority, such as activities carried out by ships flying under the flag of a flag State(21)Ibid n59, paragraphs 247 and 360. When addressing the subsequent qualification, namely that the activity may cause “substantial pollution of or significant and harmful changes to the marine environment”(22)Article 206 UNCLOS; and ibid n59 paragraph 362, the Tribunal in the COSIS Advisory Opinion held the view that the inclusion of the word “or” allows for two alternative thresholds for triggering the obligation to conduct an EIA - the first alternative is based on the wording “substantial pollution” while the second threshold is based on “significant and harmful changes”(23)Article 206 UNCLOS. Ultimately, the Tribunal highlighted that Article 206 does not outline the contents of an EIA nor a specific procedure, but that the wording “as far as practicable”(24)Article 206 UNCLOS (which comes into play after an activity has met the threshold triggering the requirement that a State conducts an EIA) appears to try to take account of the differing capabilities among states to conduct EIAs.
Considering the broad interpretation adopted by ITLOS in the COSIS Advisory Opinion, Article 206 is, at least in principle, capable of applying to certain ship-related activities. At the same time, the threshold‑based and discretionary nature of Article 206, combined with the absence of any detailed procedural requirements, has raised questions as to how this general obligation operates in regulatory contexts where more specific regimes exist(25)Alla Pozdnakova, ‘The IMO and Treaties: Appraisal of the IMO’s Contribution to Future Ocean Governance’ (2024) in Laura Carballo Piñeiro and Máximo Q Mejia Jr (eds), The Elgar Companion to the Law and Practice of the International Maritime Organization (Edward Elgar Publishing 2024) 86–111, page 22. These questions are particularly relevant in relation to shipping, which is subject to a dedicated framework under Article 211, which concerns the prevention, reduction, and control of pollution from vessels and establishes a sector-specific regulatory framework for shipping. Flag States are required to adopt and enforce regulations to prevent pollution from ships flying under their flag or of their registry, and these regulations must be aligned with international standards(26)Article 211 UNCLOS. Article 211(1) also requires that States cooperate through the competent international organization, which is the IMO, for the development of these standards. Read in this context, Article 211(1) can be understood as shaping the way the general due diligence obligation from Article 206 is expected to be exercised in the shipping context, particularly in relation to vessel‑source pollution regulated through the IMO. As Henriksen has noted, Articles 206 and 211(1) of UNCLOS reflect different regulatory logics which complicate the application of EIA obligations to shipping - Article 206 is directed at “planned activities” constituting identifiable environmental risks, a concept which, as Henriksen notes, does not ordinarily capture routine vessel operations(27)Tore Henriksen, ‘Regulating shipping under conditions of uncertainty: The Arctic Ocean and knowledge-based decision-making’ (2023) Research Handbook on International Marine Environmental Law. 2nd edition, page 5. By contrast, Article 211(1) places vessel-source pollution within a sector-specific framework through the IMO. In a similar vein, Pozdnakova observes that the existence of this specialised regime supports the argument that the general EIA obligation under Article 206 may arguably not extend to shipping, which is instead governed primarily through internationally agreed standards developed within the IMO framework(28)Ibid n72, page 22 . Together, these observations illustrate the different regulatory logics underpinning Articles 206 and 211(1), which has traditionally complicated the application of EIA obligations to shipping.
Viewed holistically, flag States comply with their obligations under UNCLOS by regulating, supervising, and enforcing pollution‑related standards for vessels flying their flag, rather than by guaranteeing that no pollution will ever occur from their vessels operating on the high seas. When read together, these provisions illustrate how UNCLOS attempts to accommodate States’ exercise of high seas freedoms while also imposing obligations aimed at the protection of the marine environment.