Cataracts of the Nile

The cataracts of the Nile are areas between Aswan and Khartoum where the water is shallow and flows quickly. The surface is broken by numerous small boulders and stones that lie on the river bed, as well as many small rocky islets. This is called "rapids or "white water".
River cataracts often go with a rapid down-drop of the river. They block the waterway, since boats cannot safely carry cargo though.
The six first cataracts of the River Nile were the main obstacles for boats sailing on the Nile in antiquity. Counted upstream (from north to south), the First Cataract is in modern Egypt; the rest are in Sudan.
The word cataract comes from the Greek word "Katarakhtes" meaning "waterfall".
In ancient times, Upper Egypt extended from the Nile Delta to the first cataract. Further upstream, in what is modern Sudan, the land was later controlled by the Kingdom of Kush.
The cataract faces north, not south, because the river flows north, from Lake Victoria in the south.
The 1899 book "The River War" by Winston Churchill explains each of the cataracts.