The data of COD_Mn,NH_3—N,TP,TN,Chla,and pH were collected at the 12 monitoring points in Caohu Lake.Then,the spatiotemporal characteristics of water environment and their causes were analyzed.Results showed that the trends of COD_Mn and TP in the lake were in a slight fluctuation from 1995 to 2007,but there were significant decreases in TN and NH_3—N.Chla had no obvious change except in 2003.Compared between the periods from 1995 to 1999 and from 2000 to 2007,the area of higher COD_Mn concentration was enlarged in the west lake from 2000 to 2007 and the area of TP was reduced in the west lake at the same period.The area of higher NH_3—N concentration migrated from the Paihe River inlet to Qiaonan area.TN and Chla concentrations in the west lake were higher than those in the east lake,but pH was high in Huailin in the east lake.In a word,water environment in the east lake was better than that in the west lake and water environment in the two lake areas has improved in recent years.The causes for the spatiotemporal characteristics of water environment in Chaohu Lake are possibly the point source pollution from industrialization,non-point source pollution from agriculture and living pollution from city,increased eutrophication by the steadily increased endogenous release,and a growth environment easy to induce water bloom and bad water environment.