The impoundment of TGR transformed the downstream part of tributary into a typical bay, but the upstream still kept the river property, such as the Daning River (Fig. 1) (Zheng, 2007). Studies of this river have focused on eutrophication (Zhong et al., 2005), the seasonal succession of phytoplankton composition and the mechanism of algal bloom formation (Zhang et al., 2010), and the role of nutrient concentrations on phyto- plankton succession (Zhou et al., 2007). Phytoplankton structure in the Daning River was studied in these documents, but little information on function groups and its relationship with hydrologic characters could be obtained. Reynolds (1999) considered that there were the same principles that influence phytoplankton composition in reservoirs and lakes, even though these two types of water body are significantly different from each other limnologically and hydrologically. As to the Daning River after TGR's impoundment, the complex hydrological conditions made it different from the typical reservoir and lake; actually, it also dif- fered from the traditional opinion on river. Up to now, there were few documents on the phytoplankton function group in such a complex water body. We assumed that hydrologic regime would be the main driving force acting on biomass and composition of phytoplankton in the Daning River. Therefore, the intention of this contribution is to survey the dynamics of phytoplankton using the functional group approach, and identify how the hydrologic regime structured the functional groups over temporal and spatial scales.