The Kumbukkan Oya flows 28 Km along the southern boundary to form the Kumana estuary and Villu before it flows to the sea. “Kumana Villu”, a 200 hectare swamp lake sustained by the river through a half a mile long narrow channel is subject to occasional inundation with sea water, is one of the most important bird nesting and breeding ground. Tens of thousands of migratory birds chose Kumana swamp as their destination during the months of April–July annually. There are about 450 species of birds recorded in Sri Lanka comprising endemic, resident and migrant. From that around 200 species of birds can be seen in Kumana National park. Thus it is one of the prime Bird Watching destination in the world.