A variation of chemical oxygen demands of bottom water in Lake Shinji was examined for 24 years of 1972-1995, based on the reports from Shimane Prefectural Government. A critical change of COD values in the time series occurred in 1980, which is exactly correlated with the benthic foraminiferal changes, as reported by Nomura and Yoshikawa (1995).
　An increase of Ammonia beccarii in sediment surface indicates an increase of organic matter in bottom water, which is reasonably interpreted from the view Point of COD.
　 The increased values of COD during 1980-1982 indicate that the water characters of Lake
　Shinji change to nutrients rich water, with an input of organic matter. The cause of this change might have been due to a construction of several embankments or bottom sediments dredging to reclaim the northwestern part of Lake Nakaumi, which hindered the movement of bottom water. So far as COD values indicating constant variations after 1983, such water characters do not changed to the present. However, foraminiferal occurrence indicates a continuation of increased organic matter into bottom water.