territorial waters

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun plural Navigable waters at the boundary of a state or nation that are held to be within the jurisdiction of that nation or state, especially those ocean waters lying within 3 or 12 nautical miles (about 5.6 or 22.2 kilometers) off shore.

from the GNU version of the Collaborative International Dictionary of English.

• (Internat. Law) The waters under the territorial jurisdiction of a state; specif., the belt (often called the marine belt or territorial sea) of sea subject to such jurisdiction, and subject only to the right of innocent passage by the vessels of other states.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun politics, geography A country's inland lakes and waterways as well as the portion of its coastal oceans, seas, or other adjoining bodies of water considered to fall within the political boundaries and legal jurisdiction of that country.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the waters surrounding a nation and its territories over which that nation exercises sovereign jurisdiction