Cascade hydropower development disrupts the continuity of natural river water temperature

leading to a significant cumulative effect on the temperature and a series of ecological effects. This study examines the water temperature along the lower Jinsha River and in the Three Gorges reservoir area

and reveals its spatial and temporal variations on different scales before and after dam construction and the cumulative effects. The impact of water temperature changes on fish spawning is also discussed. The results show that after the Xiluodu and Xiangjiaba dams were constructed

the annual mean water temperature difference along the lower Jinsha becomes smaller; along the river

the annual highest temperature at the hydrological stations shows a decreasing trend

while the annual lowest is significantly elevated

especially in January and December. After the construction

the annual temperature variation is reduced

and the time period featuring water temperature distribution has a trend of ‘convergence’－the days of water temperature distribution changed from M-type to V-type. An examination on the cumulative effect indicator finds that after dam construction

a significant time crowding effect occurs－a lag time in the extreme water temperature

water temperature delayed up to 1 - 2 months

the fish of 48% and 44% affected to a high degree at the Panzhihua section and the section downstream of Xiangjiaba dam respectively－thereby affecting severely the fish spawning and reproduction in the downstream and the fish protection sections. The study demonstrates the cumulative effects of water temperature impacted by cascade dam construction and its impact on fish spawning

laying a basis to enhance the role of temperature changes caused by large-scale cascade dams and the downstream ecological restoration.