Streams enter Lough Barra from Crockfadda and Moylenanav. From there the River Gweebarra flows southwestwards between the Derryveagh Mountains and Glendowan Mountains, crossing the R252 at Doocharry. From here it widens, being bridged by the N56 south of Lettermacaward. It enters the Gweebarra Bay which flows on into the North Atlantic Ocean.