Border irregularities of the United States

Border irregularities of the United States, particularly panhandles and highway incursions into other jurisdictions, are shown here. Often they are a result of borders which do not conform to geological features.

There are several exclaves between the United States and Canada, including the entire state of Alaska. Other exclaves include the Northwest Angle, Point Roberts and Akwesasne.

The status of the waters around Nunez Rocks is disputed. Nunez Rocks is a low-tide elevation ("bare at half-tide") area (LTE) that is south of a line known as the "A-B" Line, which was defined in a 1903 arbitration decision on the Alaska–Canada boundary. The court specified the initial boundary point (Point "A") at the northern end of Dixon Entrance and Point "B" 72 nautical miles (83 mi; 133 km) to the east. Canada relies on the "A-B" Line as rendering nearly all of Dixon Entrance as Canadian internal waters. The U.S. does not recognize the "A-B" Line as an official boundary, instead regarding it as allocating sovereignty over the land masses within the Dixon Entrance, with Canada's land south of the line. The U.S. regards the waters as subject to international marine law, and in 1977 it defined an equidistant territorial sea throughout Dixon Entrance. This territory, which surrounds Nunez Rocks, extends south of the "A-B" line for the most part. The United States has not ratified the Law of the Sea Treaty, although it adheres to most of its principles as customary international law. Under the treaty, LTEs may be used as basepoints for a territorial sea, and the U.S. uses Nunez Rocks as a basepoint. As a non-signatory, however, there is nothing preventing the U.S. from claiming areas beyond the scope of the Law of the Sea Treaty. The fact remains that, for about half of each day, above-water territory that Canada regards as Canadian is surrounded by sea territory that the U.S. has declared to be American.

In Texas and Mexico, shifts in the course of the lower Rio Grande have created numerous pene-exclaves. Under the Boundary Treaty of 1970 and earlier treaties, the United States and Mexico have maintained the actual course of the river as the international boundary, but both must approve proposed changes. From 1989 to 2009, there were 128 locations where the river changed course, causing land that had been on one side of the river to then occupy the opposite bank. Until the boundary is officially changed, there are 60 small pene-exclaves of the state of Texas now lying on the southern side of the river, as well as 68 such pene-exclaves of Mexico on the northern side of the river.

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