Low-tide elevation

A low-tide elevation is defined in Article 13 of the United Nations Convention on the Law of the Sea (UNCLOS) as a naturally formed area of land that is surrounded by and above water at low tide but submerged at high tide.¹ This definition excludes artificial structures and requires the feature to be naturally formed. Under UNCLOS, a low-tide elevation does not have a territorial sea of its own, but if it lies wholly or partly within the breadth of the territorial sea measured from the mainland or an island, it may be used as a baseline for measuring the territorial sea.² If it lies beyond that distance, it has no territorial sea of its own, and its presence does not affect the delimitation of maritime zones.

The legal treatment of low-tide elevations significantly impacts the delimitation of maritime boundaries between states with opposite or adjacent coasts. In the 2009 case Maritime Delimitation in the Black Sea (Romania v. Ukraine), the International Court of Justice (ICJ) considered the status of Serpents' Island, which is an island, and the surrounding low-tide elevations, ruling that they could not be used to shift the provisional equidistance line.³ Similarly, in the 2012 Bangladesh/Myanmar case, the International Tribunal for the Law of the Sea (ITLOS) held that low-tide elevations located within the territorial sea of a coastal state can be used as basepoints, but those beyond cannot.⁴ These decisions illustrate that low-tide elevations have a limited but sometimes decisive role in determining maritime entitlements.

The classification of a coastal feature as a low-tide elevation, an island, or a rock has profound legal consequences. Under Article 121 of UNCLOS, an island is a naturally formed area of land that is above water at high tide and can generate a territorial sea, exclusive economic zone, and continental shelf, whereas a rock that cannot sustain human habitation or economic life generates only a territorial sea.¹ Low-tide elevations, being submerged at high tide, are not islands and cannot generate any maritime zones of their own, except as basepoints when within the territorial sea of a coastal state. This distinction has been central in disputes such as the South China Sea arbitration, where the tribunal determined that features like Scarborough Shoal are low-tide elevations and therefore cannot generate exclusive economic zone entitlements.⁵

Beyond the headline cases, several lesser-known aspects of low-tide elevations shape state practice. For instance, the 1958 Convention on the Territorial Sea and the Contiguous Zone first codified the concept, which was later refined in UNCLOS.⁶ In the 2014 arbitration between Croatia and Slovenia, the tribunal addressed the status of low-tide elevations in the Gulf of Piran, though the case was ultimately decided on other grounds.⁷ Additionally, low-tide elevations can be affected by sea-level rise, potentially altering their legal status and maritime boundaries, a topic of growing scholarly debate. Some states, such as the United States, have taken the position that low-tide elevations may be used as basepoints even if they are not within the territorial sea, a view not widely shared.⁶

Territorial sea

A belt of coastal waters extending up to 12 nautical miles from the baseline, over which the coastal state has sovereignty.

Baseline

The line from which the breadth of the territorial sea is measured, normally the low-water line along the coast.

Equidistance line

A line every point of which is equidistant from the nearest points on the baselines of two states, used in maritime delimitation.

Exclusive economic zone

A sea zone extending 200 nautical miles from the baseline, where the coastal state has sovereign rights over natural resources.