Glossary
Maximum and average depth
Maximum depth is the depth at the deepest point of a lake. Average depth is the lake's volume divided by its area. A lake can have a great maximum depth but a shallow average depth if only a small part of it is deep.
How depth is measured
The Geospatial Information Authority of Japan (GSI) carries out a Lake Survey that maps the beds of major lakes. An echo sounder on a survey boat sends sound waves to the lake bed and measures depth from the time they take to return. The boat's position is fixed by satellite (GNSS), and the speed of sound in water and changes in water level are measured to correct the values. The results are compiled into lake charts with depth contours.
This catalog uses the GSI figures (the depth in the list of surveyed lakes) for the 26 Hokkaido lakes covered by the GSI survey, and the 1991 national lake survey for the rest. Values can differ with the survey year and method.
Japan's deepest lakes
In the 1991 national lake survey, Japan's deepest lake was Lake Tazawa in Akita (423 m), followed by Hokkaido's Lake Shikotsu and Lake Towada on the Aomori–Akita border. All of the top five are caldera lakes formed by volcanic activity, and caldera lakes also top the list by average depth.
On the other hand, half of Japan's lakes had a maximum depth of less than 5 m, and 96% were 50 m or less. By average depth, 78% were under 5 m and 90% under 10 m. Deep lakes are rare.
Hokkaido's deepest lakes
- Lake Shikotsu 360.1 m (caldera lake)
- Lake Mashu 211.4 m (caldera lake)
- Lake Toya 179.7 m (caldera lake)
- Lake Kuttara 148 m (caldera lake)
- Lake Kussharo 117.5 m (caldera lake)