Pyramid Lake, 188 sq mi (487 sq km), W Nev. The lake, a remnant of ancient Lake Lahontan, receives the Truckee River. Visited (1844) by U.S. explorer John Frémont, the lake was named for its large pyramidal rocks. It is located in the Pyramid Lake (Native American) reservation. In the lake is Anaho Island, a national wildlife refuge.