Mahaweli River (Ganga) is the longest in the Island originating in the hills and winding around and through the Kandy district before falling into the Indian Ocean at Trincomalee in the East after a 350km run. On its way with dams here and there, the diversion of its flow now helps irrigational efforts especially to boost the farming peasants. The Victoria Dam project off Kandy is supposed to be one of the largest in Asia.
Kelani Ganga that comes into the border of Colombo and then to the Sea, a 145km course. This too originates on the south western hillsides; to be precise, at the Adam’s Peak mountainside. It is broader than the Mahaweli at some points. It also supplies sufficient moisture to the rainforests on its way. For a tourist, it might be of interest if he/ she are visiting Kitulgala forest for white water rafting and camping site as the river runs nearby besides other rivulets and smaller kinds.
Again, on the West, below Colombo is the 129 km Kalu Ganga which flows with relatively a slower current and thus expert canoeing is not required for the eco-tourists. It also passes through the Gem City, Ratnapura before reaching Kalutara near Colombo where you find a famous Buddhist Temple as well. Along its course however, are the chirps and shrills of birds as the path comes along eco-rich areas. There are at certain points where the water rapidly flows but with a trained guide one can get instructions beforehand.