Abstract: This paper dews with the physico-chemical properties of lake water and their seasonal changes during 1997—1998 in upper and middle reaches of the Changjiang River. The result are summarized as follows: 1. The normal conditions of water quality were: Water temperature was 16.93℃, S ecchi transparency (cm)—damming before was 11, damming after was 19.57. pH damm ing before was 8.4, damming after was 8.14. conductivity was 322.5μs/cm. Alkali nity, as CaCO3 was 118.69mg/l. Hardenss was 9.26 Germany Degree. Chemical oxyg en demand was 1.84mg/l.; 2. The contents (mg/l) of nutrient elements were: NH4-N 0.226, NO2-N 0.023, NO3-N 0.748, Total nitrogen 1.299, Total phosphorus 0.194, PO4-P0.049, silic ate 3.898.