The Kelani River (කැළණි ගඟ) is a 145-kilometer-long (90 mi) river in Sri Lanka. It ranks as the fourth-longest and one of the main rivers in the country, originated from the Sri Pada Mountain Range to Colombo. Along its course, it passes through or borders several Sri Lankan districts, including Nuwara Eliya, Ratnapura, Kegalle, Gampaha, and Colombo itself. The Kelani River has two main tributaries in its upper reaches: the Kehelgamu Oya and the Maskeli Oya. These tributaries contribute to hydroelectric production in Sri Lanka, with major reservoirs and power stations along their course. Notable reservoirs include Castlereigh Reservoir, Norton Reservoir, Maskeliya Reservoir, Canyon Reservoir, and Laxapana Reservoir. The Kelani River supplies approximately 80% of the water used in Colombo, making it crucial for the capital city. Beyond drinking water, the river serves transportation, fisheries, and hydroelectricity production.