Based on a result of the assemblage analysis of benthic foraminifera in Lake Shinji，2 Assemblages of 7 Subassemblages were recognized．The foraminifera assemblages are controlled by the distribution of water mass in Lake Shinji．Miliammina Assemblage is distributed under the influence of Shinji Lake Surface Water．Ammonia Assemblage is distributed under the influence of intermediate saline water mass included Shinji Lake Bottom Water．Poor or no Foraminifera Facies are distributed in < 3 m water depth in the Shinji Lake Surface Water and in area under the influence of fresh water in Hii River．The distribution of foraminifera assemblage is varying by the change of water quality（salinity，water temperature and dissolved oxygen）in water mass and the movement of water mass．
The increase of Ammonia“beccarii”is recognaized during the investigation（August 1992 to June 1993）．This phenomenon is compared to Ammonia event proposed by Nomura and Endo（1998）．Although it was considered that ammonia event occured around the year 1980 in Lake Shinji and Lake Nakaumi，the result of this study suggests that the appearance of Ammonia event in the western part ofLake Shinji has a time lag about 12 years．