The Maduganga river is a shallow water body in south-west Sri Lanka, which enters the sea at Balapitiya
The Buddhist Amarapura Nikaya sect had its first upasampada (higher ordination ceremony) on a fleet of boats anchored upon it in 1803. The Buddhist Kothduwa temple is situated on an isolated island in the lake.
Together with the smaller Randombe Lake, to which it is connected by two narrow channels, it forms the Madu Ganga wetland. Its estuary and the many mangrove islets on it constitute a complex coastal wetland ecosystem. In has high ecological, biological and aesthetic significance, being home to 303 species of plants belonging to 95 families and to 248 species of vertebrate animals. It might be one of the last remaining tracts of pristine mangrove forests in Sri Lanka
The inhabitants of its islets produce peeled cinnamon and cinnamon oil.
The Maduganga Wetland was declared in 2003, in terms of the Ramsar Convention.