An international water law is an agreement between two or more nations that regulates activity on the seas. Most international laws come into effect after the participating nations sign a treaty. A treaty is an international agreement between two or more nations in written form and governed by international law.

United Nations Law of the Sea

Until the twentieth century, nations did not have the ability to protect their coastlines and waters for a great distance. Nations also did not require or have the ability to use vast amounts of ocean resources, such as fish or crude oil. For these reasons nations observed only a 3-mile (4.8-kilometer) territorial water zone until 1900. A territorial water zone is an area off the coast or on a nation's border in which a nation can defend and enforce its laws.

By 1850, military progress enabled...