Lake Shikotsu is a typical crater lake situated in the western part of the island of Hokkaido. The lake was created approximately 32,000 years ago, originally in a circular shape with a diameter of 12 km. Its present shape was achieved by the activity of surrounding volcanoes such as Mt. Eniwa, Mt. Fuppushi and Mt. Tarumai. The lake has a mean water depth of 266 m and the water volume is so large for its surface area that it rarely freezes in winter, despite an average temperature of -5deg C. Thus L. Shikotsu and neighboring L. Toya represent the northern boundary of distribution of non-freezing lakes in Japan.

The lake is typically oligotrophic. A transparency value of 25 m was recorded in 1926. From 1927 to 1929, a large amounts of nitrogen and phosphorus were introduced into the lake to help the breeding of kokanee salmon (Oncorhynchus nerka) transplanted from L. Akan. Between 1973 and 1979, however, the maximum and average transparency still amounted to 38.5 m and 20 m, respectively, indicating that the water quality has been fairly stable during the past 50 years.

In the Winter Olympic Games of 1972, a downhill race was held on Mt. Eniwa and the road system from the city of Sapporo was well improved. With the subsequent completion of lakeside roads, people now enjoy recreation, camping and field sports in the magnificent natural environs of Shikotsu-Toya National Park.