It flows northwestward and empties to Bombetoka Bay, forming a large delta.

The river carries an enormous amount of reddish-orange silt to the sea.

[4] Removal of the native forest for cultivation and pastureland during the past 50 years has led to massive annual soil losses approaching 250 metric tonnes per hectare (112 tons per acre) in some regions of the island, the largest amount recorded anywhere in the world.

Several fish species are endemic to the river basin, including the three cichlids Paretroplus petiti, P. tsimoly and P. maculatus.

The Betsiboka's largest tributary, the Ikopa River, drains the capital city of Antananarivo.