The Nile

The Nile is one of the most famous rivers anywhere on our planet, and rightfully so. While all rivers are important for people and wildlife who live nearby, the Nile looms especially large, both literally and figuratively. As arguably the longest river in the world, it has been the lifeblood of civilizations for millennia. Its waters have supported agriculture, fostered trade, and inspired countless myths and stories throughout history.

Here are a few reasons why this river is so influential—and interesting.

1. It’s the longest river on Earth.

The Nile flows north for about 6,650 kilometers (4,132 miles), from the African Great Lakes through the Sahara desert before emptying into the Mediterranean Sea. It goes through 11 countries: Tanzania, Uganda, Rwanda, Burundi, the Democratic Republic of the Congo, Kenya, Ethiopia, Eritrea, South Sudan, Sudan, and Egypt, and it drains 3.3 million square kilometers (1.3 million miles), or about 10% of the African continent. (The map here, a composite of NASA satellite images, spans from Lake Victoria to the Nile Delta.)

The Nile is widely considered Earth’s longest river, but that title isn’t as simple as it sounds. Aside from just measuring, it also depends on how we decide where each begins and ends, which can be tricky in big, complex river systems.

Scientists tend to go by the longest continuous channel in a system, but that may still leave room for ambiguity. The Nile is only slightly longer than the Amazon River, for example, and in 2007 a team of Brazilian scientists announced they had remeasured the Amazon and found it to be 6,800 km (4,225 miles) long, thus dethroning the Nile. Their study wasn’t published, though, and many scientists are skeptical about its methods. The Nile is still generally credited as the world’s longest river by sources from the United Nations to the Guinness Book of World Records, although the Amazon also boasts plenty of superlatives, including the world’s largest river by volume since it holds about 20% of Earth’s freshwater.

2. There’s more than one Nile.

The Lower Nile historically flooded in the summer, which mystified early Egyptians, especially since it rarely rained where they lived. We now know, however, that despite being one river in Egypt, the Nile is fed by much rainier places to the south, and its hydrology is driven by at least two “hydraulic regimes” upstream.

The Nile has three main tributaries: the White Nile, the Blue Nile, and the Atbara. The White Nile is the longest, starting with streams that flow into Lake Victoria, the world’s largest tropical lake. It emerges as the Victoria Nile, then traverses swampy Lake Kyoga and Murchison (Kabalega) Falls before reaching Lake Albert (Mwitanzige). It continues north as the Albert Nile (Mobutu), later becoming the Mountain Nile (Bahr al Jabal) in South Sudan, and joins the Gazelle River (Bahr el Ghazal), after which it’s called the White Nile (Bahr al Abyad). It finally becomes just “the Nile” near Khartoum, Sudan, where it meets the Blue Nile.

The White Nile flows steadily all year, while the Blue Nile fits most of its work into a few wild months each summer. Along with the nearby Atbara, its water comes from the highlands of Ethiopia, where monsoon patterns cause both rivers to shift between a summer torrent and winter trickle. The White Nile may be longer and steadier, but the Blue Nile supplies nearly 60% of the water that reaches Egypt each year, mostly during summer. The Atbara joins in later with 10% of the Nile’s total flow, almost all of which arrives between July and October. It was these rains that flooded the Nile each year in Egypt, and because they eroded basalt lavas on their way out of Ethiopia, their water turned out to be especially valuable downstream.

3. People spent centuries searching for its source.

Ancient Egyptians revered the Nile as their source of life, but it was inevitably shrouded in mystery. It would be for centuries, too, as expeditions repeatedly failed to find its source, with Egyptians, Greeks, and Romans often foiled by a region called the Sudd (in what’s now South Sudan), where the Nile forms a vast swamp. This fed the river’s mystique, and it’s why classical Greek and Roman art sometimes portrayed it as a god with a hidden face.

The Blue Nile gave up its secrets first, and an expedition from ancient Egypt may have even traced it back to Ethiopia. The White Nile’s source proved much more elusive, though, despite many efforts to find it—including those by Scottish explorer David Livingstone, who was rescued from one mission in 1871 by Welsh journalist Henry Morton Stanley, via the famous quote “Dr. Livingstone, I presume?” European explorers had only recently found Lake Victoria, and after Livingstone died in 1873, Stanley was one of many who helped confirm its link to the Nile, along with the prolific East African guide and explorer Sidi Mubarak Bombay.

The search still hadn’t ended, however. The White Nile begins even before Lake Victoria, although not everyone agrees where. There is the Kagera River, which flows into Lake Victoria from Lake Rweru in Burundi, but it too receives water from two other tributaries: the Ruvubu and the Nyabarongo, which flows into Lake Rweru. The Nyabarongo is also fed by the Mbirurume and Mwogo rivers, which arise from Rwanda’s Nyungwe Forest, and some consider this to be the farthest source of the Nile.

4. It takes a strange detour in the desert.

After stubbornly pushing north for most of its course, the Nile takes a surprising turn in the midst of the Sahara. With its main tributaries finally united, it continues north through Sudan for a while, then abruptly turns southwest and starts flowing away from the sea. It goes on like this for about 300 km (186 miles), as if it’s heading back to Central Africa instead of Egypt.

It eventually gets back on track, of course, and crosses Egypt as one of the most famous and influential rivers on Earth. But why does it take such a big detour first? Known as the “Great Bend,” this is one of several features caused by a huge underground rock formation called the Nubian Swell. Formed by tectonic uplift over millions of years, it forced this dramatic curve and formed the cataracts of the Nile. If not for the relatively recent uplift by the Nubian Swell, “these rocky river stretches would have been quickly reduced by the abrasive action of the sediment-laden Nile,” according to a geological overview by the University of Texas at Dallas.

5. Its mud helped shape human history.

As it winds into Egypt, the Nile transforms a swath of Sahara desert along its banks. This contrast is visible from space, where a long, green oasis can be seen hugging the river amid the bleakly tan landscape around it.

The Sahara is the largest hot desert on Earth, smaller only than our two polar deserts, and it’s no small feat to change it this way. Thanks to its seasonal influx of water from Ethiopia, the Lower Nile has historically flooded in summer, soaking the desert soil in its floodplain. But the water didn’t tame the Sahara alone. The Nile also brought a secret ingredient: all the sediment it collected along the way, mainly black silt eroded by the Blue Nile and Atbara from basalt in Ethiopia. Those silty floodwaters would surge into Egypt each summer, then dry up and leave behind a miraculous black mud.