Notable in the development of the law of the sea are a number of international conventions signed in the latter half of the 20th century. The United Nations (UN) held its first Conference on the Law of the Sea (UNCLOS I) in 1956, which resulted in a 1958 Convention. The final conference, held in Montego Bay, Jamaica, in 1982, resulted in the 1982 Law of the Sea Convention (LOSC). The LOSC came into force in 1994 upon receiving the necessary number of UN signatories.
While the United States ratified the 1958 Convention, as of late 2013, it had not become a party to the 1982 Convention. The United States recognizes that the 1982 Convention reflects customary international law and complies with its provisions.
NOAA is responsible for depicting on its nautical charts the limits of the 12 nautical mile Territorial Sea, 24 nautical mile Contiguous Zone, and 200 nautical mile Exclusive Economic Zone (EEZ). Each of these maritime zones is projected from what is called a “normal baseline,” which is derived from NOAA nautical charts. A “normal baseline” is defined under the Law of the Sea as the low-water line along the coast as marked on officially recognized, large-scale charts or the lowest charted datum, which is mean lower low water (MLLW) in the United States. The method of arriving at this baseline is described in the 1958 Convention and in the 1982 Convention. The U.S. normal baselines are ambulatory and subject to changes such as accretion (addition of land) and erosion. Unless the seaward boundary or zone is fixed, it will be subject to corresponding change.
The location of maritime zones and boundaries can have potentially far-reaching effects. As a result, NOAA works with other federal agencies, particularly the U.S. Department of State, to periodically update U.S. maritime zones and boundaries as depicted on NOAA navigational charts.