The so-called "Nishina Three Lakes", L. Aoki, L. Nakatsuna and L. Kizaki, are a chain of tectonic lakes about 30,000 years old. They are situated at the eastern foot of the Japanese Northern Alps along the remarkable tectonic zone or Fossa Magna which traverses the main island (Honshu) of Japan. L. Aoki (maximum depth 58 m) is oligotrophic, L. Nakatsuna (maximum depth 12 m) is eutrophic, and L. Kizaki (maximum depth 29.5 m) is mesotrophic, although these lakes are arranged linearly from north to south along the same water system. The trophic level of the water is apparently inversely correlated with depth. Since such nutritional dynamics lend themselves to comparative limnology, many studies have been carried out on the Nishina Three Lakes since the first voluminous work by A. Tanaka, "Studies on the Lakes of the Japanese Northern Alps (1930)".

The water level of L. Aoki in winter has been lowered by about 20 m since 1954, owing to the use of its water for power generation. Provision was also made to introduce cold water from a neighboring river running down from the Japanese Alps, thus radically changing the aquatic environment of L. Aoki. The water level of L. Kizaki also becomes lower by about 3 m in winter, and is recovered in spring by channeling water from L. Aoki. The transparency in L. Kizaki averaged about 5 m until 1950, but decreased to approximately 3 m since 1970. From the end of the 1970's, Anabaena has bloomed annually in July- August, and the coloration of surface water has also become frequent due to the increase of microorganisms which graze upon Anabaena. These evidences suggest that the trophic level of this lake has recently changed from mesotrophic to eutrophic.