The Akita Prefectural Fisheries Experiment Station survey indicated a depth of 413 meters in 1926 using a wire rope.

The survey also found two small volcanic cones and sedimentation deposits to the depth of around one kilometer on the north-west side of the lake bottom.

These findings lend credence to the theory that the lake is indeed of volcanic origin, from an explosive eruption of 1.4 million years ago.

However, after the acidic content of the lake changed in 1940, the only surviving fish is the dace, while most of the other species, including the kunimasu, are thought to have gone extinct.

The statue of Tatsuko by Yasutake Funakoshi stands with her back to the clear blue waters, a figure of pureness and beauty, and was unveiled on May 12, 1968.