Territorial Waters, Explained
Under the UN Convention on the Law of the Sea, a coastal state's sovereignty runs 12 nautical miles from its baselines (the territorial sea), enforcement powers for customs and immigration extend to 24 nm (the contiguous zone), and exclusive rights to fish, energy and seabed resources reach 200 nm (the EEZ). Beyond that lie the high seas — and whether a speck of land generates those zones at all turns on whether it's legally an island or merely a rock.
The bands: 12, 24, 200
Sea law is a set of concentric bands measured in nautical miles from the coast's baselines. The territorial sea reaches 12 nm: here the coastal state is sovereign — its criminal law applies, its rules govern, and the sovereignty extends to the airspace above and the seabed below. The one carve-out is innocent passage: foreign ships may transit, continuously and expeditiously, so long as they don't fish, spy, pollute or threaten — submarines must surface and show their flag.
From 12 to 24 nm runs the contiguous zone, a policing buffer: the state can't legislate there, but it can enforce its customs, fiscal, immigration and sanitary laws — board the smuggler before the cargo lands. And out to 200 nm stretches the Exclusive Economic Zone: not sovereignty but exclusive rights — to the fish, the wind, the oil and everything else of economic value in the water column and seabed. Foreign vessels still enjoy freedom of navigation through an EEZ; they just can't take the tuna. Beyond 200 nm (plus continental-shelf extensions for the seabed) are the high seas, open to all flags.
Where the measuring starts: baselines
Every band is measured from the baseline, and the default is refreshingly physical: the low-water line along the coast, as marked on the state's official large-scale charts — the same line a chart datum defines. Waters landward of the baseline (harbours, estuaries, many bays) are internal waters, where even innocent passage doesn't apply.
Where coasts are deeply indented or fringed with islands — Norway's fjords, Indonesia's seventeen thousand islands — states may draw straight baselines connecting outer points, sweeping large sea areas into internal or archipelagic waters. The choice of baseline moves every subsequent line by the same amount, which is why baseline claims are among the most litigated details in the law of the sea: push the start line 30 nm seaward and you've moved 30 nm of EEZ with it.
Article 121: why a rock is not an island
The highest-stakes sentence in UNCLOS is Article 121(3): “Rocks which cannot sustain human habitation or economic life of their own shall have no exclusive economic zone or continental shelf.” A legal island — naturally formed, above water at high tide, capable of sustaining habitation or economic life — generates the full set: 12 nm territorial sea and a 200 nm EEZ, which for a mid-ocean island means roughly 125,000 square nautical miles of exclusive rights. A rock gets the 12 nm territorial sea only. A low-tide elevation — dry only at low water — generates nothing of its own.
That one distinction explains decades of curious behaviour: states garrisoning specks, building lighthouses and desalination plants on reefs, and arguing that a guano outcrop hosts 'economic life'. It also explains why artificial construction doesn't help — UNCLOS is explicit that artificial islands generate no zones, and the 2016 South China Sea arbitration held that no amount of land reclamation upgrades a feature's original status. When you look at the world's remotest islets — the kind our island destinations guide visits — you're often looking at the anchor point of an EEZ larger than the country that owns it.
What the bands mean in practice
For anyone who actually goes to sea, the bands translate simply. Inside 12 nm you're in someone's country: their fishing licences, their dive-permit rules, their marine-park fees (every permit in our diving destinations guide operates here), their right to stop and board. In the 12–24 nm ring, expect customs and immigration enforcement but local law doesn't otherwise reach you. Across the EEZ, navigation is free but resources are spoken for — the fine for fishing someone's EEZ without a licence can be the boat itself. And on the high seas, your flag state's law travels with the vessel: a British-flagged yacht in the mid-Atlantic is a small floating piece of British jurisdiction.
One nuance worth knowing: the bands are measured in nautical miles precisely because the nautical mile is a minute of latitude — the zones were drawn to be walkable with dividers on the same charts that define the baselines. The law and the chart share a unit by design.