Lake Tōya

Lake Tōya (洞爺湖, Tōya-ko) is a volcanic caldera lake in Shikotsu-Toya National Park, Hokkaidō, Japan. It is part of the "Japanese volcanic belt" and is located in the southwestern part of Hokkaidō. The lake is nearly circular, approximately 10 kilometers (6.2 miles) in diameter, and has a surface area of 70.7 square kilometers (27.3 sq mi). The maximum depth is 179 meters (587 ft).

Lake Tōya is known for its clear water, scenic beauty, and year-round unfrozen surface due to geothermal activity. Nakajima Island, consisting of four islands, is located in the center of the lake. These islands are the remnants of a volcanic cone that formed after the initial caldera formation.

The surrounding area is a popular tourist destination, offering hot spring resorts (onsen), hiking trails, and views of nearby Mount Yōtei, an almost perfectly conical stratovolcano often likened to Mount Fuji. The area also features active volcanism, including Mount Usu, which has erupted several times in recorded history. The latest significant eruption of Mount Usu occurred in 2000, causing significant ashfall and prompting evacuations.

The lake and its surrounding area are significant both geologically and recreationally. The history of volcanic activity and the ongoing geothermal activity make it a valuable site for scientific study. Additionally, its scenic beauty and recreational opportunities contribute significantly to the local economy.