Taihu Lake, one of the five largest freshwater lakes in China, is situated in the middle of the Yangtze River Delta, which is inhabited by more than 100 million people and provides one seventh of China, s Gross National Product.Marine and brackish organisms found at the bottom (275cm, about 11280 a B.P.) of the sediment core indicates that sea water intruded to the lowland areas and river valleys of the present western Taihu Lake during the last major rise in sea level.The sea water intrusion to Taihu Lake occured 2000 years ago earlier than previously indicated.Evidence also shows that sea water intrusion was limited, affecting only a part of the present Taihu Lake.Evidence from the lake sediment analysis suggests that this lake underwent major changes from a brackish to a freshwater environment between 5000 and 5300 a B.P.Major changes in sediment were noted between 35-45cm (5070-5330 a B.P.) reflecting a period during which inorganic carbon was drastically reduced, primary production (Chl.a and pigments) increased significantly, and many marine and brackish organisms disappeared and were replaced by freshwater forms.This evidence indicates that prior to,5cm, Taihu Lake received constant inputs of sea water, and perhaps existed as a bay or an estuary.After that period, the water gradually became fresh.At depths above 35cm, Taihu Lake turned completed lacustrian under Increasing impact of wind-driven lake currents, and expanded substfintially to reach its present size.This lake was oligotrophic, the eutrophic conditions in the present lake developed during recent decades as a result of increased nutrient loadings.