Yellowstone Lake is the largest body of water in Yellowstone National Park. The lake is 7,732 feet above sea level and covers 136 square miles with 110 miles of shoreline. While the average depth of the lake is 139 ft, its greatest depth is at least 394 ft. Yellowstone Lake is the largest freshwater lake above 7,000 ft in North America. In winter, ice nearly 3 ft thick covers much of the lake except where shallow water covers hot springs.