The lake is long with 73 percent of the lake's surface area in Quebec, where it drains into the Magog River. However, three-quarters of its watershed, , is in Vermont. The total is , with located in Quebec. In Vermont, the lake lies in parts of the towns of Derby and Newport, in addition to the City of Newport, all in Orleans County. In Quebec, the lake lies in parts of Austin, Magog, Ogden, Potton, Saint-Benoît-du-Lac, and Stanstead Township, all in Memphrémagog Regional County Municipality. The lake occupies most of what the Vermont Agency of Natural Resources calls "Basin 17". At the very south end of the lake, there is the South Bay, connected by the narrowest part of the lake.