Lake Tōya (Japanese: とうやこ) is located in Hokkaido, Japan, spanning Tōyako Town in Abuta District and Sobetsu Town in Usu District. It belongs to the Osarugawa River system, a Class 2 river. The area surrounding Lake Tōya, together with Shikotsu-Tōya National Park, forms the Tōya-Usu UNESCO Global Geopark, which has been selected as a Japanese Geopark, a Global Geopark, one of Japan's Top 100 Scenic Spots, one of the "New 100 Travel Destinations in Japan," and one of the "500 Beautiful Towns in Japan to Visit."
Lake Tōya is situated in southwestern Hokkaido and was formed by the collapse of a volcanic caldera. It is the ninth largest lake in Japan and the third largest caldera lake, after Lake Kussharo and Lake Shikotsu. The lake spans approximately 11 kilometers from east to west and about 9 kilometers from north to south, forming an almost circular shape. Along the southern shore are popular tourist spots such as Lake Tōya Hot Springs, Mount Usu, and Shōwa-shinzan, making the area a major tourist destination in Hokkaido.
The largest island at the center of the lake is called Nakajima, covering an area of about 4.85 square kilometers, with its highest point reaching 455 meters above sea level. Administratively, the eastern and southeastern areas of the lake belong to Sobetsu Town, while the rest falls under the jurisdiction of Tōyako Town.
As for the origin of the name, "Tōya" (とうや) derives from the Ainu language term "to-ya" (ト・ヤ), meaning "lakeside." Originally, it was the name for the northern lakeshore area. Later, Japanese settlers referred to the area as "Mukō-Tōya" ("Facing Tōya"), and eventually adopted "Tōya" as the name of the lake. In the Ainu language, the lake itself was called "kim-un-to" (キム・ウン・ト), meaning "lake in the mountains." Locally, "Tōya" is sometimes also pronounced as "Dōya."
