Usually cited as the longest river in the world, the Nile flows about 4,132 miles in a generally south-to-north direction from its headwaters in Burundi to Egypt's Mediterranean Sea coast, where it forms a prototypical delta. Over 80% of the Nile's flow comes from the shorter Blue Nile headstream, which arises from Ethiopia's Lake Tana and meets the longer White Nile — whose headwaters include Lake Victoria — at Khartoum. At the first of the Nile's six cataracts is the Aswan High Dam, which forms Lake Nasser and greatly reduces the annual floods.