List of areas disputed by Canada and the United States
Although Canada and the United States share the longest border between two countries, there is a long history of disputes about the border's demarcation.
Machias Seal Island (about 8.1 ha (20 acres)) and North Rock (Maine / New Brunswick), located in what is known as the "Grey Zone" (about 717 km2 (277 sq mi) in size), is occupied by a Canadian lighthouse but claimed by the United States and visited by U.S. tour boats. The area is patrolled by the Canadian Coast Guard. The unresolved maritime boundary breaks into two elements: the sovereignty of the island and the location of the maritime boundary taking into account who is the rightful owner of the island.
Strait of Juan de Fuca (Washington / British Columbia): At the mouth of the strait, both countries declared fishing zones in 1977. Each country used a mildly differing method to define an equidistant water boundary. The two separate water areas in dispute amount to about 51.5 km2 (19.9 sq mi).
Yukon–Alaska dispute, Beaufort Sea (Alaska / Yukon) Canada supports an extension into the sea of the land boundary between Yukon and Alaska. The U.S. does not, but instead supports an extended sea boundary into the Canadian portion of the Beaufort Sea. Such a demarcation means that a minor portion of Northwest Territories EEZ in the polar region is claimed by Alaska, because the EEZ boundary between Northwest Territories and Yukon follows a straight north-south line into the sea. The U.S. claims would create a triangular shaped EEZ for Yukon/Canada. The disputed area is about 21,440 km2 (8,280 sq mi) in size. The precise translation of a phrase in the Anglo-Russian Convention of 1825, which was written in French, is part of the issue. The convention makes reference to the 141st Meridian "in its prolongation as far as the Frozen ocean." The authentic text is in French: "dans son [sic] prolongation jusqu’à la Mer Glaciale." The precise question is the interpretation that should be given to the preposition "jusqu’à." Specifically, is it inclusive or exclusive of the object to which the preposition relates?
Northwest Passage: Canada claims the passage as part of its "internal waters" belonging to Canada, while the United States regards it as an "international strait" (a strait accommodating open international traffic). The Canadian Coast Guard and Royal Canadian Navy have commissioned a new ice breaker along with multiple offshore patrol ships to guard and patrol the waters.
Dixon Entrance (Alaska / British Columbia) contains two water areas that are mutually claimed by Canada and the U.S. A line known as the "A-B" Line 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 also designated Point "B" 72 NM to the east. Canada relies on the "A-B" line as rendering nearly all of Dixon Entrance as its 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 line throughout Dixon Entrance, mainly to the south of the "A-B" line. The intersecting lines create four separate water areas with differing claim status. The two areas south of the "A-B" line (about 2,789 km2 (1,077 sq mi) and 51.5 km2 (19.9 sq mi) in size) are claimed by both countries. The other two water areas are north of the "A-B" line and are not claimed by either country. The two unclaimed areas are about 72 km2 (28 sq mi) and 1.4 km2 (0.5 sq mi) in size. In addition, Nunez Rocks is a low-tide elevation ("bare at half-tide") that lies south of the "A-B" Line, surrounded by the sea territory claimed by the U.S. 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.