Lake Memphremagog is a glacial freshwater lake stretching between Newport, Vermont, and Magog, Quebec, with most of its waters in Canada but much of its watershed in Vermont. Shaped by ice and fed by four Vermont rivers, it is notable for its depth, islands, cross-border geography, and role as a drinking water source for about 200,000 people. Within Abenaki territory long before modern settlement, it later figured in 18th-century military movements and 19th-century steamship travel linking communities on both sides of the border. Today it remains important for navigation, water management, and ongoing environmental protection against runoff, pollution, and invasive species.