To explore the factors regulating seasonal variation of total suspended solids (TSS) and its two fractions in a giant dendritic reservoir (the Three-Gorges Reservoir of China, TGR) in the subtropical monsoon region, suspended solids, chlorophyll a (a surrogate for lake internal processes) and water residence time (an index of hydrologic flushing) were examined monthly from August 2005 to July 2006. TSS ranged from 0.6 to 200.3 mg/L and from 0.6 to 78 mg/L respectively in the mainstream and in a typical reservoir-bay (the Xiangxi Bay) of the TGR,. TSS exhibited a typical seasonal pattern in the mainstream rather than in the Xiangxi Bay of the TGR. The fraction of non-volatile suspended solids (NVSS) was often more dominant in the mainstream than in the Xiangxi Bay, especially during the flood season. Regressions analysis showed that 87.6% and 89.8% of seasonal variation in TSS and NVSS of the mainstream, respectively, are explained by water residence time. In contrast, suspended solids (particularly volatile suspended solids, VSS) of the Xiangxi Bay displayed significant correlation with algal biomass, and no correlation with hydrological parameters. It implies that the Xiangxi Bay was a more autochthonous system than the mainstream of the TGR where exogenous influences were the more determinant factors. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.