Large rivers in the Amazon can be taken over by smaller ones in a slow process called fluvial piracy. The Uraricoera River is being captured by its tributary, the Uraricaá River, in the Branco River Basin. This takeover is happening because of erosion caused by sinking land near the Branco and Negro rivers. This process is slow and can take hundreds of years to finish. The capture usually happens just before the two rivers meet.