MNN By RUSSELL MCLENDON
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 drains 3.3 million square kilometers (1.3 million miles), or about 10% of the African continent. (The map at right, 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 as LiveScience points out, 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.
A view of Tis Abay, or Blue Nile Falls, in Ethiopia. (Photo: Alberto Loyo/Shutterstock)
The Lower Nile historically flooded in summer, which mystified early Egyptians, especially since it almost never 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, Blue Nile and 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.
A sign proclaims the farthest source of the Nile in Rwanda’s Nyungwe rainforest. (Photo: Jose Cendon/AFP/Getty Images)
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’s death 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 cite this as the farthest source of the Nile.
4. It takes a strange detour in the desert.
This true-color image, captured by NASA’s Terra satellite, shows the Nile’s ‘Great Bend’ in Sudan. (Photo: Jacques Descloitres, MODIS Land Rapid Response Team/NASA/GSFC)
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 relatively recent uplift by the Nubian Swell, “these rocky rivers 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.
This satellite view highlights the contrast between the green vegetation along the Nile and the surrounding Sahara. (Photo: Jacques Descloitres, MODIS Rapid Response Team/NASA Goddard Space Flight Center)
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 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.
The Nile River nurtures a long, narrow oasis through the Sahara. (Photo: Mirko Kuzmanovic/Shutterstock)
Permanent human settlements first appeared on the Nile’s banks around 6000 BCE, according to the nonprofit Ancient History Encyclopedia (AHE), and by 3150 BCE, those settlements had become “the world’s first recognizable nation state.” A complex and distinct culture quickly developed, and for nearly 3,000 years, Egypt would remain the preeminent nation in the Mediterranean world, fueled by water and fertile land it received as gifts from the Nile.
Egypt was eventually conquered and eclipsed by other empires, yet despite its decline, it still thrives with help from the Nile. It’s now home to nearly 100 million people — 95% of whom live within a few kilometers of the Nile — making it the third most populous country in Africa. And since it also teems with relics of its heyday, like elaborate pyramids and well-preserved mummies, it continues to reveal ancient secrets and capture modern imaginations. All this would’ve been nearly impossible in this desert without the Nile, and considering the role Egypt has played in the rise of civilization, the Nile has influenced human history in a way few rivers have.
6. It’s a haven for wildlife, too.
A hippopotamus yawns in the Nile River. (Photo: Mathias Sunke/Shutterstock)
Humans are just one of many species who rely on the Nile, which flows through (and influences) a variety of ecosystems along its course. Closer to the White Nile’s headwaters, the river plies biodiverse tropical rainforests teeming with plants like banana trees, bamboo, coffee shrubs and ebony, to name a few. It reaches mixed woodland and savanna farther north, with sparser trees and more grasses and shrubs. It becomes a sprawling swamp in the Sudanese plains during the rainy season, especially the legendary Sudd in South Sudan, which spans nearly 260,000 square km (100,000 square miles). Vegetation continues to fade as it moves north, finally all but vanishing as the river arrives in the desert.
One of the most notable Nile plants is papyrus, an aquatic flowering sedge that grows as tall reeds in shallow water. These are the plants that ancient Egyptians famously used to make paper (and from which the English word “paper” is derived) as well as cloths, cords, mats, sails and other materials. It once was a common part of the river’s native vegetation, and while it still grows naturally in Egypt, it’s reportedly less common in the wild today.
A thicket of papyrus grows along the Victoria Nile in Uganda. (Photo: Oleg Znamenskiy/Shutterstock)
As with its plant life, the animals living in and around the Nile are far too numerous to adequately list here. There are its many fish, for instance, including Nile perch as well as barbels, catfish, eels, elephant-snout fish, lungfish, tilapia and tigerfish. An abundance of birds live along the river, too, and its waters are also a vital resource for many migrating flocks. The Nile Delta, in fact, is “part of one of the world’s most important migration routes for birds,” according to the WWF.
The Nile also supports several large animal species, such as hippopotamuses, which were once common along much of the river, but now mostly inhabit the Sudd and other swampy areas in South Sudan. There are also soft-shelled turtles, cobras, black mambas, water snakes and three species of monitor lizards, which reportedly average 1.8 meters (6 feet) in length. Perhaps the river’s most famous fauna, however, is the Nile crocodile. These inhabit most parts of the river, according to Encyclopedia Britannica, and are one of the largest crocodilian species on Earth, growing up to 6 meters (20 feet) long.
7. It was home to a crocodile god and a Crocodile City.
The pyramids at Giza near the banks of the Nile, pictured here circa 1900. (Photo: Hulton Archive/Getty Images)
As ancient Egypt grew along the Lower Nile, the river’s importance was not lost on its people, who made it a central theme of their society. Ancient Egyptians knew the Nile as Ḥ’pī or Iteru, meaning simply “river,” but it was also called Ar or Aur, meaning “black,” in honor of its life-giving mud. They correctly saw it as their source of life, and it played a key role in many of their most important myths.
The Milky Way was seen as a celestial mirror of the Nile, for example, and the sun god Ra was believed to drive his ship across it. It was thought to embody the god Hapi, who blessed the land with life, as well as Ma’at, who represented the concepts of truth, harmony and balance, according to the AHE. It was also associated with Hathor, a goddess of the sky, women, fertility and love.
Nile crocodiles are the largest freshwater predators in Africa. (Photo: Johan Swanepoel/Shutterstock)
In one popular myth, the god Osiris is betrayed by his jealous brother Set, who tricks him into lying down in a sarcophagus, pretending it’s a gift. Set then traps Osiris inside and throws him in the Nile, which carries him away to Byblos. Osiris’ body is eventually found by his wife, Isis, who retrieves him and tries to bring him back to life. Set intervenes, though, stealing Osiris’ body, chopping it into pieces and scattering them across Egypt. Isis still tracks down every piece of Osiris — all except for his penis, which had been eaten by a Nile crocodile. That’s why crocodiles were associated with the god of fertility, Sobek, the AHE explains, and this event was seen as the catalyst that made the Nile so fertile. Due to this story, the AHE adds, anyone eaten by a crocodile in ancient Egypt “was considered fortunate in a happy death.”
The reverence for Nile crocodiles was particularly strong in the ancient city of Shedet (now called Faiyum), located in the river’s Faiyum Oasis south of Cairo. This city was known to the Greeks as “Crocodilopolis,” since its residents not only worshipped Sobek, but also honored an earthly manifestation of the god: a living crocodile named “Petsuchos,” whom they covered in jewelry and kept in a temple, according to The Guardian. When one Petsuchos died, a new crocodile filled the role.
8. It may be a window to the real underworld.
Aside from the underworld of ancient Egyptian mythology, the Nile may also hold secrets about a more literal underworld. (Photo: Sergey73/Shutterstock)
Osiris couldn’t come back to life without his whole body, according to the AHE, so he instead became god of the dead and lord of the underworld. The Nile was seen as a gateway to the afterlife, with the eastern side representing life and the western side considered the land of the dead. Yet while the river abounds with ancient links to the spiritual underworld of ancient Egypt, modern science suggests it may also serve as a window to a more tangible underworld: the Earth’s mantle.
There is some debate over the Nile’s age, but in late 2019, a team of researchers reported that Nile drainage has been stable for about 30 million years — or five times longer than previously thought. In other words, if you traveled along the Nile during the Oligocene Epoch, its course would be eerily similar to the route we know today. That’s because of a stable topographic gradient along the river’s path, the researchers explain, which apparently held steady for so long due to currents circulating in the mantle, the layer of hot rock under Earth’s crust.
In essence, the Nile’s path has been maintained all this time by a plume of mantle that mirrors the river’s northward flow, the study suggests. The idea of mantle plumes shaping topography on the surface isn’t new, as Eos magazine points out, but the huge scale of the Nile basin could illuminate this relationship like never before. “Because the river is so long, it offers a unique opportunity to study these interactions on a landscape-wide scale,” one of the study’s authors tells Eos. And based on what the Nile can reveal about the mantle below, this might help scientists use it and other rivers as “windows into the underworld,” as Gizmodo put it, potentially shedding new light on the inner workings of our planet.
9. It’s changing.
A view of the Aswan High Dam, captured by an astronaut aboard the International Space Station. (Photo: NASA)
People have left their mark along the Nile for millennia, but the dynamic has changed a bit lately. One big shift came in 1970 with completion of the Aswan High Dam, which impounds the river in southern Egypt to create a reservoir called Lake Nasser. For the first time in history, this gave humans control over the Nile’s life-giving floods. It offers “enormous benefits to the economy of Egypt,” according to Encyclopedia Britannica, since water can now be released where and when it’s needed most, and since the dam’s 12 turbines can generate 2.1 gigawatts of electricity.
The dam has also changed the Nile in negative ways, however. The black silt that tamed the Sahara, for example, is now largely impounded behind the dam, accumulating in the reservoir and canals instead of flowing north. Silt used to enrich and expand the Nile Delta over time, but it’s now shrinking due to erosion along the Mediterranean coast, according to National Geographic. The dam has also led to a gradual decline in the fertility and productivity of riverside farmland, Britannica adds, noting that “Egypt’s annual application of about 1 million tons of artificial fertilizers is an inadequate substitute for the 40 million tons of silt formerly deposited annually by the Nile flood.” Offshore from the delta, fish populations have reportedly declined due to loss of nutrients once delivered by Nile silt.
Sudan also has some older dams along Nile tributaries, like the Blue Nile’s Sennar Dam, which opened in 1925, or the Atbara’s Khashm el-Girba Dam, which opened in 1964. These may not alter the river quite like the Aswan High Dam, but a project in Ethiopia has raised new fears over water supplies downstream.
The Grand Ethiopian Renaissance Dam, pictured here in December 2019, is expected to be Africa’s largest hydropower plant once it’s fully operational. (Photo: Eduardo Soteras/AFP/Getty Images)
Located on the Blue Nile, the $5 billion Grand Ethiopian Renaissance Dam (GERD) has been under construction since 2011, and is expected to generate 6.45 gigawatts once it’s fully operational in 2022. That could make a huge difference for Ethiopia, where about 75% of people lack access to electricity, and selling excess electricity to nearby countries could reportedly bring the country $1 billion per year.
To deliver those benefits, however, the dam will need to hold back lots of water that would otherwise flow to Sudan and Egypt. That has stirred anxiety in those countries, both of which are already prone to water shortages, given the scale of the project. The dam will create a reservoir more than double the size of Lake Mead — the largest reservoir in the U.S., held behind the Hoover Dam — and will eventually hold 74 billion cubic feet of water from the Blue Nile, according to Yale Environment 360. Filling the reservoir could take anywhere from five to 15 years.
“During this period of fill, the Nile’s fresh water flow to Egypt may be cut by 25%, with a loss of a third of the electricity generated by the Aswan High Dam,” researchers reported in GSA Today, a journal published by the Geological Society of America. Many in Egypt worry the dam will also limit water supplies long after the reservoir is filled, compounding other problems related to population growth, water pollution, land subsidence and climate change, along with the ongoing loss of silt at Aswan.
A view of the Nile in Cairo’s southern suburb of Kozzika. (Photo: Amir Makar/AFP/Getty Images)
Egypt, Ethiopia and Sudan have made little progress despite nearly a decade of on-and-off negotiations, although they did reach an initial deal at a January 2020 meeting. That was a “breakthrough” in the long-running dispute, according to Egypt Today, and the three countries are now holding follow-up talks in hopes of finally solidifying a “comprehensive, cooperative and sustainable agreement.”
That’s promising, although there are still a lot of details for the countries to work out. Plus, as the GSA Today study pointed out, the dilemma of how to share dwindling water among fast-growing populations will continue regardless of what happens with these negotiations. Both Ethiopia and Sudan have proposed more Nile dams, it notes, and with some 400 million people living in countries along the Nile — many of whom already experience droughts and energy shortages — there’s a good chance even more water will need to remain upriver in coming years.
The sun sets over the White Nile in Uganda. (Photo: Rod Waddington [CC BY-SA 2.0]/Flickr)
It’s hard to overstate the Nile’s importance to people and wildlife throughout its basin. Despite maintaining its path for millions of years, and despite all it has already seen from our species in the last few millennia, it now faces unprecedented pressure from human activities all along its route. It’s only one river system, but as one of the most famous and influential waterways on Earth, it has come to symbolize something even bigger than itself: interconnectedness. Humans rely on countless rivers all over the planet, yet if we continually fail them when they’re in trouble — even big, iconic rivers like the Nile — we should probably expect the same from them.