Kalu Ganga (literally: Black River) is a river in Sri Lanka. The river originates from Sri Pada Peak Wilderness Sanctuary, reaching the sea at Kalutara after a 129 km journey. The Black River flows through the Ratnapura and the Kalutara District and passes the city Ratnapura. The mountainous forests in the Central Province and the Sinharaja Forest Reserve are the main sources of water for the river. The Edwardian manor, Richmond Castle is on the banks of the river near Kalutara.