Casa Robino

Initially, a country's sovereign territorial waters extended 3 nautical miles or 6 km (range of cannon shot) beyond the shore. In modern times, a country's sovereign territorial waters extend to 12 nautical miles (~19 km) beyond the shore. In the early 1970s, Ecuador claimed territorial waters extending to 200 nautical miles. They began seizing U.S. tuna-fishing boats and charging heavy fines (that the U.S. government paid). Eventually the U.S. agreed to submit the issue to the International Court of Justice at The Hague.[5] This eventually led to the recognition of 12 nautical miles as normal for the territorial sea/waters and international recognition of the 200 mile exclusive economic zone by the Third United Nations Convention on the Law of the Sea in 1982.
Part V, Article 55 of the Convention states:
Specific legal regime of the exclusive economic zone
The exclusive economic zone is an area beyond and adjacent to the territorial sea, subject to the specific legal regime established in this Part, under which the rights and jurisdiction of the coastal State and the rights and freedoms of other States are governed by the relevant provisions of this Convention.