Lake area

A lake's area is the extent of its water surface. The figure depends on which water level is measured and where inflowing rivers are cut off, so each survey has its own rules.

How area is measured

• GSI Area Statistics: the Geospatial Information Authority of Japan measures and publishes the areas of prefectures and municipalities from its base maps, and lists the areas of lakes of 1 km² or more at the same time. The 2026 edition gives values as of July 1.
• National lake survey: a lake is defined as the area covered by still water at its highest water level, excluding inflowing and outflowing rivers. The survey covered the main natural lakes, in principle those of 1 ha (0.01 km²) or more.

This catalog uses the 2026 Area Statistics for the 30 lakes of 1 km² or more that it lists, and the 1991 lake survey for smaller lakes.

9 of Japan's 20 largest lakes are in Hokkaido

In the 2026 Area Statistics, Japan's largest lake is Lake Biwa (669.22 km²), followed by Lake Kasumigaura (168.20 km²) and Hokkaido's Lake Saroma (151.63 km²). 9 of the top 20 are in Hokkaido.

Most lakes are small

In the 1991 lake survey, 77% of Japan's lakes were 1 km² or smaller, and small lakes of 0.01 to 0.1 km² alone made up 48%. The well-known large lakes are only a small fraction; most lakes are small ponds.