The Gal Oya is a 108 km (67 mi) long river, in South east Sri Lanka. It is the 16th longest river in Sri Lanka.
The river was dammed in 1948 as part of the Gal Oya scheme. The dam created the Senanayake Samudra — the largest reservoir in Sri Lanka.The Gal Oya project resulted in the formation of the 100,000 acre Gal Oya basin. This basin has since been used for cultivating paddy, chillies, sugarcane and potatoes.
The Gal Oya National Park in the vicinity has a wide variety of wildlife including bears, leopards and elephants.