Abstract: The impact of reservoir operation on water environment within the reservoir area is a hot topic for watershed ecological protection, especially for the near-dam section environment which directly affects the the downstream ecological environmental. In this study, a field monitoring of hydrology and water quality was conducted simultaneously in the near-dam section of the Shuikou Reservoir, to reveal the spatial distributions of key water quality physicochemical indexes and the main influencing factors under the condition of guaranteed 50% flow discharge rate. The observational results suggested a typical horizontal and vertical circulation pattern in the area, because the average near-dam rates of flow were measured as 1 420 and 1 440 m³·s^-1, respectively, while the rates of discharge from the dam were comparably lower with 1 227 and 1 207 m³·s^-1, respectively. The spatial distributions of the physical and chemical water quality indicators were primarily affected by both vertical and horizontal circulations in the reservoir area. The study area was featured with excessive TN, severe hypoxia in the middle and bottom layers, and excessive TP in the surface and bottom layers. The S3 section, located at 5.5 km upstream of the Shuikou Dam, was particularly eutrophic at the bottom. The distribution of water quality physicochemical indexes in the near-dam area was mainly affected by water temperature and blue-green algae abundance.

Key words: near-dam section of reservoir, hydrological guarantee rate, water environment, eutrophication