Who Owns the Sea? Territorial Waters and Exclusive Economic Zones Explained

A political map of the world colours the land and leaves the sea blank, which is misleading. Most of the ocean surface sits inside some legal zone, and those zones determine who fishes, who drills, who lays cable and who may simply sail through. The rules are unusually tidy for international law, because they are geometric: almost everything is a distance measured outward from a baseline along the coast.

This piece describes the structure, not any particular dispute. The structure is the durable part, and once you can see it, a large amount of maritime news becomes legible without any commentary attached.

From cannon shot to convention

For centuries the working answer to how far a state's waters extended was practical rather than legal: as far as it could enforce. The eighteenth-century convention, often attributed to the Dutch jurist Cornelius van Bynkershoek, was the cannon-shot rule, roughly three nautical miles, on the reasoning that control ended where artillery did. It was arbitrary but stable, and it lasted while ships were slow, fishing was coastal and the seabed was unreachable.

Three things broke it: industrial fishing fleets that could strip a coastal shelf, offshore oil that made the seabed valuable, and the arrival of many newly independent coastal states after 1945 with an interest in claiming more than three miles. The result was the Third United Nations Conference on the Law of the Sea, which ran through the 1970s and produced the UN Convention on the Law of the Sea, signed in 1982 and in force from 1994. UNCLOS is the framework almost every discussion of maritime rights now runs on, including by states that have not ratified it but broadly follow its zones in practice.

The bands, from shore outward

Baselines and internal waters

Everything is measured from a baseline, normally the low-water line along the coast, with straight baselines permitted across bays, river mouths and deeply indented or island-fringed coasts. Water landward of the baseline, including ports, most bays and rivers, is internal waters. Here the state's authority is essentially the same as on land, and there is no general right of foreign entry.

The territorial sea: 12 nautical miles

Out to twelve nautical miles the coastal state has sovereignty over the water, the seabed beneath and the airspace above. The single large qualification is innocent passage: foreign ships may transit continuously and expeditiously provided they do nothing prejudicial to the coastal state's peace, security or good order. Fishing, surveying, spying and weapons exercises are not innocent. Simply sailing through is. In straits used for international navigation, a stronger regime called transit passage applies, which is why narrow waterways carry different rules from open coastline. Several of the world's busiest are covered in our piece on maritime chokepoints.

The contiguous zone: 24 nautical miles

Between twelve and twenty-four miles the state has no sovereignty but may enforce a limited list of laws: customs, immigration, taxation and sanitary rules. It is a buffer for interdiction rather than a claim of ownership. In practice it is the zone where smuggling and irregular-entry enforcement happens.

The exclusive economic zone: 200 nautical miles

The EEZ is the band most often misunderstood. Out to two hundred nautical miles the coastal state holds sovereign rights over exploring and exploiting natural resources: fish, oil, gas and seabed minerals, plus jurisdiction over marine scientific research, artificial islands and environmental protection. It does not own the water. Foreign vessels retain freedom of navigation and overflight, and may lay submarine cables and pipelines subject to the coastal state's rules on the shelf.

That single distinction, resource rights rather than territory, resolves most apparent contradictions in maritime reporting. A warship transiting an EEZ is doing something normal. A foreign trawler fishing in it is not.

The continental shelf, and beyond 200 miles

Rights to the seabed follow their own logic. Every coastal state has continental-shelf rights to at least two hundred miles, and where the natural prolongation of its landmass extends further it can claim an extended shelf, up to limits defined by sediment thickness and distance, by submitting evidence to the Commission on the Limits of the Continental Shelf. These claims concern the seabed and subsoil only, never the water column above. This is why polar seabed mapping has become so active, a thread we pick up in Arctic shipping routes.

The high seas and the Area

Beyond all national zones lie the high seas, open to navigation, overflight, fishing, cable-laying and research by every state, with vessels governed mainly by the law of the flag they fly. The seabed beyond national jurisdiction is called the Area and is administered by the International Seabed Authority as common heritage, which is why deep-sea mining licences are issued internationally rather than nationally.

Why small islands command enormous zones

Because the zones are measured from coastline, not scaled to landmass, a scattering of small islands can generate a maritime area larger than a continental state. Pacific island nations are the clearest case: modest land areas paired with some of the largest EEZs in the world, and fishing-licence revenue as a result. UNCLOS distinguishes islands, which can sustain human habitation or economic life and generate a full EEZ, from rocks, which cannot and generate only a territorial sea. That definitional line carries more economic weight than almost any other sentence in the convention.

The same geometry explains features that look unrelated. Fishing fleets cluster at EEZ boundaries because a line on water is where access changes. Undersea cables, which carry effectively all intercontinental data, are routed with shelf jurisdiction and permitting in mind. Seabed mining interest concentrates where extended shelf claims or ISA licences allow it. Ports and hubs still form where routes are forced to converge, the pattern behind why port cities rule the world.

Why this is worth knowing

Maritime zones are one of those frameworks that quietly explain a whole category of headlines: a fisheries argument, a cable-repair delay, a survey-ship standoff, a mining licence. None of it requires taking a side to understand, because the underlying grid is arithmetic applied to coastline. Geography sets the shape, and the law mostly formalises it.

The sea is not owned so much as layered, and each layer grants a different verb: govern, police, extract, or merely pass.