Abstract: The water quality of Shanghu Lake and Kuncheng Lake in Changshu City of Jiangsu Province was monitored and evaluated in 2018—2019 to understand the water quality of major urban lakes. The results showed that the differences of water transparency （SD）, total nitrogen （TN）, total dissolved nitrogen （TDN） and total dissolved phosphorus （TDP） between the two lakes were significant （P<0.05）, and the differences of total phosphorus （TP） and dissolved organic carbon （DOC） between the two lakes were extremely significant （P<0.01）. There were obvious seasonal changes of water quality in two lakes, and the water quality of Shanghu Lake was good in spring and autumn, but deteriorated in summer and winter, while that of Kuncheng Lake was poor in spring and summer, and the pollution was aggravated in autumn and winter. Based on single factor index evaluation, the main pollution factors in Shanghu Lake and Kuncheng Lake were the same, both of which were TN and TP, and the water quality of Shanghu Lake all year was class Ⅲ, while Kuncheng Lake was inferior class V. The Nemero index of Shanghu Lake ranged from 0.50 to 0.87, indicating that the lake was relatively clean all year, while that of Kuncheng Lake ranged from 1.37 to 2.31, indicating that the lake was slightly polluted all year. The comprehensive nutrient index of Shanghu Lake ranged from 45.78 to 49.02, indicating a moderate vegetative state all year, while that of Kuncheng Lake ranged from 54.31 to 59.23, indicating a mild eutrophication state all year.

Key words: water eutrophication, urban lake, Shanghu Lake, Kuncheng Lake, evaluation method, Changshu City