Lake Akan, Volcanic lake in Kushiro, Japan

Lake Akan is a volcanic lake in Kushiro that spans approximately 13 square kilometers at 420 meters elevation. Four islands sit within the water, and forested shores surround the entire basin.

Lake Akan began as a caldera lake formed by eruptions about 175,000 and 158,000 years ago. Later eruptions of Mount Meakan filled part of it, and around 10,000 years ago the growth of Mount Oakan dammed the remainder, splitting the old lake into today's Akan, Penketo and Panketo. Meakan remains active, with a small eruption on 21 March 2006.

The Ainu kotan on the hot-spring shore of Lake Akan holds about 30 households and roughly 120 residents, the largest Ainu settlement in Hokkaido. Its name comes from the Ainu word akam, meaning wheel. Dancers perform traditional dances at the Onnechise hall, and two museums, the Ainu Life Memorial Hall and the Forest and Lake Art Museum, display the culture alongside shops selling woodcarvings. Since 17 June 2017 the Irankarapte Music Festival has been held at the Ikor theater; irankarapte is an Ainu greeting.

Several bus services connect the lake to central Kushiro, located about 75 kilometers south, with multiple daily departures available. The journey is straightforward and well-organized.

The lake houses marimo algae that naturally form into large green spheres comparable to soccer balls over centuries. Visitors often discover these unusual organisms are a surprising feature of the water.