The Gal Oya is a 108 km (67 mi) long river, in southeast Sri Lanka.

[1] It begins in the hills east of Badulla and flows northeast, emptying into the Indian Ocean south of Kalmunai.

The dam created the Senanayake Samudra — the largest reservoir in Sri Lanka, at Bintenne.

Resettlement of the Tamils and Sinhalese people displaced in this scheme gave rise to among the first ethnic riots in Sri Lanka.

The Gal Oya National Park in the vicinity has a wide variety of wildlife including bears, leopards and elephants.