Moosehead Lake is the largest lake in the U.S. state of Maine and the largest mountain lake in the eastern United States. Situated in the Longfellow Mountains in the Maine Highlands Region, the lake is the source of the Kennebec River. Towns that border the lake include Greenville to the south and Rockwood to the northwest. There are over 80 islands in the lake, the largest being Sugar Island with the almost as large Deer Island to the west.