The cataracts of the Nile are shallow stretches between Aswan and Khartoum where the water 's surface is broken by numerous small boulders and stones that lie on the river bed , as well as many small rocky islets . The cataracts of the Nile are shallow stretches of the river between Aswan and Khartoum where the water 's surface is broken by numerous small boulders and stones protruding from the river bed , as well as many small rocky islets .