Koyama-ike, Natural lake in Tottori Prefecture, Japan.

Koyama Lake is a natural body of water near Tottori City with several islands scattered across its surface. The shoreline is relatively low and the surrounding landscape opens up with views toward distant hills.

The lake formed when sand dunes cut off an ancient bay and created a lagoon separated from the sea. Over time, this geography drew human settlement to its shores.

The lake is known for the Koyama长者 legend: a wealthy landowner who owned vast rice paddies, unable to finish planting before sunset, used a fan to bring the sun back and finish the work; by the next morning the fields had all become a pond. A similar tale is told of Yubugawa Pond in Gifu. In the Mitsu district of Tottori, the nationally rare ishigama fishing is practiced in winter: fish hiding in stone crevices are prodded out with sticks and caught. It is a prefecture-designated intangible folk cultural property, and an ishigama festival is held during the fishing season.

The lake is walkable from Koyama Station and sits in flat, easy-to-navigate terrain. The eastern shore offers the most convenient access with parking areas and spots for a break.

In the early 1930s the lake served as a water aerodrome: a seaplane landed here on 7 September 1931, and from 1932 a route linked Koyama-ike with Kinosaki, the beginning of Tottori Prefecture's airports. At the old landing site in Katsura, only a few posts of the wooden pier remain.