Duhaime's Law Dictionary

Territorial Sea Definition:

Waters adjacent to a state's coast and subject to its sovereignty.

Related Terms: High Seas, Continental Shelf, Tidal Waters

In United States v Postal, the court used these words;

"The ... Convention on the High Seas and the Convention on the Territorial Sea and the Contiguous Zone...  set forth principles of international law governing the relations of the ratifying states with respect to territorial seas, those waters adjacent to a state's coast and subject to its sovereignty, and to the high seas, those waters lying seaward of the territorial seas and subject to the sovereignty of no state.

"The territorial sea, although defined in the Convention on the Territorial Sea and the Contiguous Zone (as those waters lying between the baseline and the line every point of which is at a distance from the nearest point of the baseline equal to the breadth of the territorial sea), is not delimited by these conventions. The limits asserted by coastal states are therefore to be judged under customary international law. The United States has long adhered to the widely accepted international rule that the territorial sea extends to three miles from the coast. The sovereignty of the coastal state extends into the territorial sea ... with the proviso that foreign vessels enjoy the right of innocent passage through it. Beyond the territorial sea lie the high seas."

The normal baseline is the low-water line along the coast, islands, rocks and even low-tide elevations as marked on large-scale charts officially recognized by the coastal state. 

In Canada:

"The territorial sea is an area of the sea that has an outer limit extending 12 nautical miles measured seaward from the baselines. The coastal state has sovereign rights over the territorial sea. Its sovereignty extends to the airspace, seabed and subsoil. In this respect, the territorial sea is similar to a state’s land territory. Ships of all states enjoy the "right of innocent passage" through the territorial sea, but they must operate under certain conditions respecting international norms. Canada has exercised jurisdiction over the territorial sea on its east and west coasts out to 12 nautical miles since 1970."1


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