Betsiboka River is a 525-kilometre (326 mi) long river in central-north Madagascar. It flows northwestward and empties to Bombetoka Bay, forming a large delta. It originates to the east of Antananarivo. The river is surrounded in mangroves. The river is distinctive for its red-coloured water, which is caused by river sediments. The river carries an enormous amount of reddish-orange silt to the sea. Much of this silt is deposited at the mouth of the river or in the bay. The Betsiboka's largest tributary, the Ikopa River, drains the capital city of Antananarivo. * * *