(also Psiol, Pesl, Pesel), a river in the RSFSR and Ukrainian SSR; a left tributary of the Dnieper. The Psel is 717 km long and drains an area of 22,800 sq km. Originating in the Central Russian Upland, it flows primarily across a hilly plain; the lower course flows through the Dnieper Lowland. The river empties into the Dneprodzerzhinsk Reservoir. The Psel is fed primarily by snow. Its floodplain is broad. Up to 70 percent of the annual flow occurs in March through May, during the high-water season. There is low water in the summer and fall. The mean flow rate 36 km from the mouth is 55 cu m per sec. The river freezes in December, and the ice breaks up between late February and early April. The main tributary is the Khorol, on the right. The cities of Oboian’, Sumy, and Gadiach are on the river.