The temporal and spatial variations of water quality in a stratified reservoir are fully dependent on the characteristics of inflow loading from its watershed and the transport regimes of pollutants after entering the reservoir. Because of the meteorological and hydrological conditions in Korea the pollutants loading to reservoirs mostly occur during rainfall events. Therefore it is important to understand the characteristics of pollutants loading from upstream rivers and their spatial propagation through the stratified reservoir during the rainfall events. The objectives of this study were to characterize the water quality variations in upstream rivers of Imha Reservoir during a rainfall event and the transport and spatial variations of pollutants in the reservoir through extensive field monitoring and laboratory analysis. The results showed that the event mean concentration of SS BOD COD_mn T-N T-P PO₄-P are 8.6~362.1 2.5~5.1 1.5~5.1 1.1~1.9 8.3~57.1 5.6~25.7 times greater than the mean concentrations of these parameters during non-rainfall period. The turbidity and SS data showed good linear correlations but the relationships between flow and SS showed large variations because of hysteresis effect during rising and falling periods of the flood. The ratio of POC to TOC were 12.6~14.7% during the non-rainfall periods but increased up to 28.2~41.7% during the flood event. The turbid flood flow formed underflow and interflow after entering the reservoir and delivered a great amount of non-point pollutants such as labile and refractory organic matters and nutrients to the metalimnion layer of reservoir which is just above the thermocline. Spatially the lateral variations of most water quality parameters were marginal but the vertical variations were significant.