Kanneliya-Dediyagala-Nakiyadeniya, Biosphere reserve in southern Sri Lanka.

Kanneliya-Dediyagala-Nakiyadeniya is a forest complex of parallel ridges and valleys in southern Sri Lanka, covering 10,139.3 hectares, with elevations from 60 to 425 metres. It is the last large rainforest in the country after Sinharaja. The Kanneliya section is mostly secondary forest regrown after logging for the Gintota plywood factory, and old tarred logging roads remain visible.

The reserve received UNESCO recognition in 2004 after logging operations halted in 1988 to protect the forests. This designation marked a shift toward formal conservation and protection of the area.

Local communities have developed deep knowledge about forest plants and their uses, passing these skills down through families for generations. This practical relationship with the woods shapes how people in the area understand and interact with their surroundings daily.

Several marked hiking trails begin from the information center in Udugama and offer different lengths and difficulty levels for various visitors. It is advisable to wear comfortable shoes and prepare for changing weather, as the forests are wet and green throughout the year.

The forest is the source of the Gin and Nilwala rivers, and more than 101 streams have been identified within it. Twenty percent of Sri Lanka's endemic freshwater fish live in these waters. The Kanneli, Nanikiththa and Udugama streams rise in Kanneliya, while Homa dola and Gal bandi dola are sourced by Nakiyadeniya and Deiyagala.