Maritime Zones and Boundaries

The maritime zones recognized under international law include internal waters, the territorial sea, the contiguous zone, the exclusive economic zone (EEZ), the continental shelf, the high seas, and the Area.  The breadth of the territorial sea, contiguous zone, and EEZ (and in some cases the continental shelf) is measured from the baseline determined in accordance with customary international law as reflected in the 1982 Law of the Sea Convention.

Maritime Zones under International Law
Maritime Zones under International Law (Image credit: U.S. Department of State)

The limits of these zones are officially depicted on NOAA nautical charts.  The limits shown on the most recent chart edition takes precedence.  For a description of the various U.S. maritime zones, as well as the Three Nautical Mile Line and Natural Resource Boundary, see the NOAA Coast Pilot (Chapter 1 in each volume) or review the information available on NOAA's  U.S. Maritime Limits & Boundaries page (source information for the NOAA nautical charts).

The boundaries of these maritime zones between coastal States are established through international agreements entered into by those nations.  For the official description of the U.S. maritime boundaries with other nations, contact the U.S. Department of State.

Additional reference information: 

Baseline

Generally speaking, the normal baseline is the low-water line along the coast as marked on large-scale charts officially recognized by the coastal State.  Special rules for determining the baseline apply in a variety of circumstances, such as with bays, ports, mouths of rivers, deeply indented coastlines, fringing reefs, and roadsteads.  Consistent with these rules, the U.S. baselines are the mean of the lower low tides as depicted on the largest-scale NOAA nautical charts.  The U.S. normal baselines are ambulatory and subject to changes as the coastline accretes and erodes.

Additional reference information: 

Internal Waters

Internal (or inland) waters are the waters on the landward side of the baseline from which the breadth of the territorial sea is measured.  The coastal State has full sovereignty over its internal waters as if they were part of its land territory and may exclude foreign flag vessels from its internal waters subject to the right of entry of vessels in distress.  The right of innocent passage does not apply in internal waters.  Ships and aircraft may not enter or overly internal waters without the permission of the coastal State. Examples of internal waters include rivers, harbors, lagoons, some bays and canals, and lakes, including the Great Lakes.

Additional reference information: 

Territorial Sea

Each coastal State may claim a territorial sea that extends seaward up to 12 nautical miles (nm) from its baselines.  The coastal State exercises sovereignty over its territorial sea, the airspace above it, and the seabed and subsoil beneath it.  Foreign flagged ships enjoy the right of innocent passage while transiting the territorial sea subject to laws and regulations adopted by the coastal State that are in conformity with the Law of the Sea Convention and other rules of international law relating to such passage.  The U.S. claimed a 12 nm territorial sea in 1988 (Presidential Proclamation No. 5928, December 27, 1988).

Additional reference information: 

Contiguous Zone

Each coastal State may claim a contiguous zone adjacent to and beyond its territorial sea that extends seaward up to 24 nm from its baselines.  In its contiguous zone, a coastal State may exercise the control necessary to prevent the infringement of its customs, fiscal, immigration, or sanitary laws and regulations within its territory or territorial sea, and punish infringement of those laws and regulations committed within its territory or territorial sea.  Additionally, in order to control trafficking in archaeological and historical objects found at sea, a coastal State may presume that their removal from the seabed of the contiguous zone without its consent is unlawful.

In 1972, the U.S. proclaimed a contiguous zone extending from 3 to 12 miles offshore (Department of State Public Notice 358, 37 Fed. Reg. 11906 (June 15, 1972)), consistent with the 1958 UN Convention on the Territorial Sea and Contiguous Zone.  In 1999, eleven years after President Reagan extended the U.S. territorial sea to 12 miles, President Clinton proclaimed a contiguous zone extending from 12 to 24 nm offshore (Presidential Proclamation No. 7219, 64 Fed. Reg. 48701 (Aug. 2, 1999)), consistent with Article 33 of the Law of the Sea Convention.

Additional reference information: 

  • Press Release by Vice-President Al Gore, "Extension of Federal Enforcement Zone in U.S. Coastal Waters Will Help Prevent Violations of Environmental, Customs, or Immigration Laws" (Sept. 2, 1999)
  • Exchange of Memoranda between the Department of State (1989) and the Department of Justice (1991) on the Extension of the Contiguous Zone to 24 nm

Exclusive Economic Zone

US EEZ limits diagramed on a globe illustration
US EEZ limits from Global Perspective (NOAA Office of Coast Survey)

Each coastal State may claim an Exclusive Economic Zone (EEZ) beyond and adjacent to its territorial sea that extends seaward up to 200 nm from its baselines (or out to a maritime boundary with another coastal State). Within its EEZ, a coastal State has: (a) sovereign rights for the purpose of exploring, exploiting, conserving and managing natural resources, whether living or nonliving, of the seabed and subsoil and the superjacent waters and with regard to other activities for the economic exploitation and exploration of the zone, such as the production of energy from the water, currents and winds; (b) jurisdiction as provided for in international law with regard to the establishment and use of artificial islands, installations, and structures, marine scientific research, and the protection and preservation of the marine environment, and (c) other rights and duties provided for under international law.

The U.S. claimed a 200 nm EEZ in 1983 (Presidential Proclamation No. 5030, 43 Fed. Reg. 10605 (Mar. 14, 1983)).  The U.S. EEZ overlaps the nation's 12 nm – 24 nm contiguous zone.  The U.S. generally recognizes claims of foreign nations to an EEZ.  See Mayaguezanos por la Salud y el Ambiente v. United States, 198 F.3d 297 (1st Cir. 1999); Koru North America v. United States, 701 F. Supp. 229, 236 n. 6 (CIT 1988).  

Note: Under certain U.S. fisheries laws, such as the Magnuson-Stevens Fishery Conservation and Management Act, the term EEZ is defined as having an inner boundary that is coterminous with the seaward (or outer) boundary of each of the individual coastal states of the U.S. See 16 U.S.C. § 1802(11). Under the Submerged Lands Act, the seaward boundary of each of the individual coastal states is generally three nautical (or geographic) miles from the coast line. The seaward boundaries of Florida (Gulf of Mexico coast only), Texas, and Puerto Rico extend nine nautical miles from the coast line. In the Great Lakes, each U.S. state’s seaward boundary may extend to the international maritime boundary with Canada. See 43 U.S.C. § 1312. Under the Submerged Lands Act, a coastal state’s seaward boundary may be fixed by Supreme Court decree. (See below for further information on the Three Nautical Mile Line and the Natural Resources Boundary.)

Additional reference information: Some of these links are to external sites.

Three Nautical Mile Line

The Three Nautical Mile Line, as measured from the territorial sea baseline and previously identified as the outer limit of the U.S. territorial sea, is retained on NOAA nautical charts because it continues to be used in certain federal laws.  Perhaps the earliest proclamation of the U.S. Three Nautical Mile territorial sea was documented by Secretary of State Thomas Jefferson, Letter to Certain Foreign Ministers of November 8, 1793 (asserting a provisional territorial sea extending a “distance of one sea-league or three geographical miles from the sea shores”) (cannon shot rule).  See also U.S. Department of State Geographic Bulletin No. 3 (Apr. 1965) (stating the longstanding position that the Territorial Sea of the United States and numerous other maritime nations concerned with the Freedom of Navigation is three nautical miles) (citing the Report of the International Law Commission, General Assembly, Official Records: 11th Sess., Supplement No. 9 (A/3159), United Nations, New York, 1956) (The term "mile " means nautical mile (1,852 meters) reckoned at sixty to one degree of latitude. Id. at 256).

Note: Since the "coast line," a term used in the Submerged Lands Act, 43 U.S.C. §1301 et seq., and the baseline are determined using the same criteria under international law, the Three Nautical Mile Line is generally the same as the seaward boundaries of individual U.S. coastal states under the Submerged Lands Act. There are exceptions; therefore, the Three Nautical Mile Line does not necessarily depict the seaward boundaries of all U.S. states in all circumstances under the Submerged Lands Act.

Natural Resources Boundary

The nine (9) nautical mile Natural Resources Boundary is the seaward limit of the submerged lands of Puerto Rico, Texas, and the Gulf coast of Florida. It coincides with the inner limit of the outer continental shelf under the Outer Continental Shelf Lands Act. See also, United States Coast Pilot.

Continental Shelf

The continental shelf of a coastal State is comprised of the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of 200 nm from its baselines where the outer edge of the continental margin does not extend up to that distance.  The extent of the continental shelf can also be limited by a maritime boundary with another coastal State.

Where the outer edge of a coastal State's continental margin extends beyond 200 nm from its baselines, the outer limits of its continental shelf are determined in accordance with Article 76 of the Law of the Sea Convention.  The portion of a coastal State's continental shelf that lies beyond the 200 nm limit is often called the extended continental shelf.

A coastal State has sovereign rights and exclusive jurisdiction over its continental shelf for the purpose of exploring it and exploiting its natural resources, as well as for other purposes specified in the Law of the Sea Convention.  The natural resources of the continental shelf consist of the mineral and other non-living resources of the seabed and subsoil together with living organisms belonging to sedentary species, that is to say, organisms which, at the harvestable stage, either are immobile on or under the seabed or are unable to move except in constant physical contact with the seabed or subsoil.

The United States proclaimed jurisdiction and control over its continental shelf in 1945 (Presidential Proclamation No. 2667 of Sept. 28, 1945).  Consistent with international law, the United States exercises its continental shelf rights out to a distance of at least 200 nautical miles through several domestic laws.  The U.S. Extended Continental Shelf Project, led by the Department of State, NOAA, and the U.S. Geological Survey, determines the outer limits of the U.S. continental shelf beyond 200 nautical miles (i.e., extended continental shelf).  In December 2023, the Department of State released the geographic coordinates defining the outer limits of the U.S. extended continental shelf.  See U.S. Dep’t of State, Announcement of U.S. Extended Continental Shelf Outer Limits (Dec. 19, 2023).

Additional reference information: 

  • United States v. Ray, 294 F. Supp. 532 (S.D. Fla. 1969), aff'd in part, rev'd in part, 423 F.2d 16 (5th Cir. 1970) (construing U.S. authority under the Outer Continental Shelf Lands Act and identifying U.S. rights and interests in the outer continental shelf)

High Seas

The high seas comprise all parts of the sea that are not included in the exclusive economic zone, the territorial sea or the internal waters of a State, or in the archipelagic waters of an archipelagic State.

Straits Used for International Navigation

Bering Sea map
Bering Sea (Worldatlas.com)

“Straits used for international navigation” are those that are used or are capable of use for international navigation between one area of the high seas or exclusive economic zone (“EEZ”) and another area of the high seas or EEZ. Part III of the Law of the Sea Convention (articles 34-45) describes the regime of transit passage through such straits and the rights, jurisdiction, and duties of the States bordering such straits. Transit passage means the exercise in accordance with Part III of the Law of the Sea Convention of the freedom of navigation and overflight solely for the purpose of continuous and expeditious transit of the strait. LOSC arts. 37, 38. The right of transit passage applies throughout straits used or capable of use for international navigation, including to all normally used approaches to and from such straits. Ships and aircraft in transit passage must comply with the duties outlined in LOSC article 39, which include proceeding without delay and refraining from any activities other than those incident to their normal modes of continuous and expeditious transit. Ships in transit passage may not carry out any research or survey activities without the prior authorization of the States bordering the strait. LOSC art. 40. States bordering straits used for international navigation may designate sea lanes and prescribe traffic separation schemes for navigation in accordance with Part III where necessary to promote safe passage of ships. LOSC art. 41. They may also adopt laws and regulations relating to transit passage in respect of certain activities, such as fishing. LOSC art. 42. The transit passage regime does not otherwise affect the legal status of the waters forming an international strait or the exercise of sovereignty or jurisdiction by the bordering States over the waters, air space, seabed, and subsoil of the strait. LOSC art. 34.

The United States considers itself a strait State (i.e., a State bordering a strait used for international navigation) and in this regard complies with the relevant provisions of international law as reflected in Part III of the Law of the Sea Convention. For example, the United States borders the Bering Strait, which connects the Bering Sea in the Pacific Ocean to the Chukchi Sea in the Arctic Ocean. Although the Bering Strait is 44 nautical miles wide at the narrowest point between the U.S. and Russian mainlands (Cape Prince of Wales, Alaska, and Cape Dezhneva, Siberia), Little Diomede Island (U.S.) and Big Diomede Island (Russia) are located midway between Cape Prince of Wales and Cape Dezhneva. The U.S.-Russia maritime boundary proceeds through the Bering Strait between Little Diomede Island and Big Diomede Island.

Additional Reference Information: 

Area

The Area is comprised of the seabed and subsoil beyond the limits of national jurisdiction. It does not include superjacent waters (i.e., the water column) or the air space above those waters. The Area and its resources are the common heritage of mankind, and no State may claim or exercise sovereignty or sovereign rights over any part of the Area or its resources. LOSC. arts. 1(1), 135-137.

Comparative Sizes of the Various Maritime Zones

Areas of the Earth covered by the Oceans approx. 335.0 million km2
High Seas 200.4 million km2
Territorial Seas 22.4 million km2
Contiguous Zones 6.6 million km2
Exclusive Economic Zones 101.9 million km2
Total areas under national jurisdiction excluding extended continental shelves beyond 200 nm 131.0 million km2

Source: UNEP/GRID-Arendal, Continental Shelf: The Last Maritime Zone at 28 (Mar. 2011).

As a measure of comparison, the mass of the contiguous United States (all states except Alaska and Hawaii) is approximately 7.7 million km2 (square kilometers).

(Updated March 25, 2024)