Lake Ikeda is a caldera lake located 40 km south of Kagoshima city; Kyūshū island, Japan. It is perhaps best known to tourists as the location of the purported sightings of a monster named Issie, and as the largest lake on Kyūshū island with a surface area of 11 km² and a shoreline length of 15 km.
Lake Ikeda is known to harbour large eels, some six feet in length. In 1998, a benthological survey was conducted in the lake, which found that there were no zoobenthos, although two tubificid oligochaetes and a chironomid were found. The lake was already considered oligotrophic until the 1940s, but one theory for the further drop in underwater life is that the existing life in Lake Ikeda has been affected by Global Warming.