The Deduru Oya (Tamil: மாயவன் ஆறு) is the sixth-longest river of Sri Lanka. The 142 km (88 mi) long river runs across four provinces and five districts.

Tributaries

  • Kospothu Oya
  • Dik Oya
  • Ratwila Ela
  • Kimbulwana Oya
  • Hakwatuna Oya
  • Maguru Oya
  • Kolamunu Oya
  • Delvita Oya

Its catchment area receives approximately 4,313 million cubic metres of rain per year, and approximately 27 percent of the water reaches the sea. It has a catchment area of 2,620 square kilometres.