Falling down the 80-metre Mahon Falls and proceeding past the "Fairy Bush", the river then passes through the village of Mahon Bridge and on past Flahavan's Mill and under the 8-arched rail bridge in Kilmacthomas. In former times, the river powered five different mills, one at Mahon Bridge, three at Kilmacthomas and one at Ballylaneen. The river is joined by the Ách Mór tributary river at Ballylaneen and ends its journey three miles further downstream at Bunmahon on Ireland's south coast. It drains into the region of the Atlantic Ocean known as the Celtic Sea.
The river is popular with whitewater kayakers. There has been no known source-to-sea descent to date but the river has been paddled from Mahon Bridge to the sea at Bonmahon by an international team of B1 and B2 kayakers in August 2012.