Champlain, Lake, a long, narrow lake forming most of the boundary between New York and Vermont and extending a short distance into Quebec. It is about 115 miles (185 km) long, up to 14 miles (23 km) wide, and as much as 400 feet (120 m) deep. Total area is about 490 square miles (1,270 km2). Lake Champlain provides part of a navigation route between the Hudson and St. Lawrence rivers. Burlington, Vermont, and Plattsburgh, New York, are the principal cities on the lake. There is a ferry service across the lake.

Lake Champlain was discovered in 1609 by Samuel de Champlain, a French explorer. It was the scene of military action in the French and Indian Wars and the American Revolution, including the American seizure of Fort Ticonderoga and the Battle of Valcour Island, where Benedict Arnold's troops were defeated by the British. In the War of 1812, an American naval force turned back the British invasion of New York in the Battle of Lake Champlain (1814).