Lake Tōya (洞爺湖, Tōya-ko) is a volcanic caldera lake in Shikotsu-Toya National Park, Abuta District, Hokkaidō, Japan. It is a part of "Toya Caldera and Usu Volcano Global Geopark" which joins in Global Geoparks Network. The stratovolcano of Mount Usu lies on the southern rim of the caldera. The lake is nearly circular, being 10 kilometers in diameter from east-west and 9 kilometers from North-South. The lake's biggest town, Tōyako is located on its western shore.