The use of excess water on identified groundwater has caused harm to the environment. Construction of reservoirs by utilizing surface water is carried out to meet water needs. The Panglima Besar Jenderal Sudirman Reservoir in Banjarnegara Regency was built to provide sufficient supply of water for agricultural and electricity. The biogeophysical dynamics of watersheds and its meteorology trigger sedimentation that threatens the sustainability of the reservoirs. This study aims to calculate the annual sedimentation rate and identify the sources of sediment in the Serayu River watershed. The study was conducted using the RUSLE method and the Sediment Delivery Ratio (SDR) was calculated using Williams Equation (1977). As a result, SDR in the Panglima Besar Jenderal Sudirman Reservoir is in the high SDR class range and the phenomenon tends to be caused by erosion on agricultural land due to massive agricultural activities in the Serayu River upstream. Land conservation in the upper reaches of Serayu River needs to be done to support the sustainability of Panglima Besar Jenderal Sudirman Reservoir.