Lake Champlain (French: lac Champlain) is a natural, freshwater lake in North America, located mainly within the borders of the United States (states of Vermont and New York) but partially situated across the Canada-United States border in the Canadian province of Quebec.

The New York portion of the Champlain Valley includes the eastern portions of Clinton County and Essex County. Most of this area is part of the Adirondack Park. There are recreational opportunities in the park and along the relatively undeveloped coastline of Lake Champlain. The cities of Plattsburgh and Burlington are to the north and the village of Ticonderoga in the southern part of the region. The Quebec portion is located in the regional county municipalities of Le Haut-Richelieu and Brome-Missisquoi.

In 2010, the estimate of cormorant population, considered a nuisance, ranged from 14,000 to 16,000. A Fish and Wildlife commissioner said that the ideal population would be 3,300 or about 3 per 1 square kilometre (0.39 sq mi). Cormorants had disappeared from the lake (and all northern lakes) due to the use of DDT in the 1940s and 1950s.

Ring-billed gulls are also considered a nuisance. Measures have been taken to reduce their population. Authorities are attempting to encourage the return of black crowned night herons, cattle egrets, great blue herons, which disappeared during the time DDT was being used.

The lake was named after the French explorer Samuel de Champlain, who encountered it in 1609. While the ports of Burlington, Vermont; Port Henry, New York; and Plattsburgh, New York are little used nowadays except by small craft, ferries and lake cruise ships, they had substantial commercial and military importance in the 18th and 19th centuries.

There is conflicting information on Native American names for the lake. Many historical works give Caniaderi Guarunte as the Iroquois name for the lake (meaning: mouth or door of the country), because the waterway was an important northern gateway to their lands. A number of other sources give Petonbowk (meaning the lake in between) as the Algonquian Abenaki name for the lake. The St. Francis/Sokoki Abenaki Band, who make their home along the Masipskiwibi (Missisquoi, "Crooked River") River in northwestern Vermont call the lake Bitawbagok, the same meaning as Petonbowk. Some recent articles appeared during the Champlain Quadricentennial (2009) claiming Ondakina as the “local” native name for the lake, but none cites a verifiable source.