Lake Suigetsu is a lake in the Hokuriku region of Honshu, Japan, which is one of the Mikata Five Lakes located in Mihama and Wakasa, Fukui Prefecture, close to the coast of the Wakasa Bay in the Sea of Japan. Since 1993, it has been attracting the attention of scientists because of the undisturbed nature of the water for many thousands of years. It is possible to identify the annual deposits of silt in a similar manner that tree rings are identified.