lake in Yellowstone National Park, northwestern Wyoming, U.S. It lies at an elevation of 7,731 feet (2,356 metres) above sea level and is the largest body of water in North America, and the second largest in the world, at so high an altitude. It is fed by 59 streams and rivers and drained by the Yellowstone River, which flows through the lake from south to north. About 20 miles (32 km) long and 14 miles (23 km) wide, the lake has a shoreline of 110 miles (177 km), a maximum depth of 390 feet (119 metres), and a surface area of 137 square miles (354 square km). It is a haven for rare species of waterbirds, including trumpeter swans, and is prized for trout fishing, although the lake's native cutthroat trout are now endangered by introduced predators.