The largest lake in Nagano Prefecture, Lake Suwa extends into the cities of Suwa and Okayashi, and Shimosuwa Town of Suwa County. It has many surrounding natural hot springs and is a designated Protected Lake.

It is said that Takeda Shingen's will stated that he was to be laid to rest in a stone coffin with his armor in Lake Suwa.

Another legend associated with Lake Suwa is the Omiwatari (御神渡), or God's Crossing/Divine Crossing. In the legend, the god Takeminakata-no Mikoto leaves his home in the Kamisha to visit his consort, the goddess Yasakatome-no Mikoto in the Shimosha, six miles away, by crossing over the frozen surface of the lake. The ice cracks with a large booming sound and juts upward. This phenomenon was observed in 2004 and on Jan. 10, 2006, where the ice thrusted up to a height of around 60 centimeters.