Lake Tazawa is a caldera lake in the city of Semboku, Akita Prefecture, northern Japan. It is the deepest lake in Japan at 423 metres (1,388 ft). The area is a popular vacation area and several hot spring resorts can be found in the hills above the lake. Akita Prefecture's largest ski area, Tazawako Ski Area [ja], overlooks the lake.

Semboku is a city located in Akita Prefecture, Japan. As of 31 January 2023, the city had an estimated population of 24,045 in 10,398 households, and a population density of 22 persons per km2. The total area of the city is 1,093.56 square kilometers (422 sq mi).