With no natural predator, scientists say, the crayfish was free to roam from where the Nile meets Egypt's Mediterranean coast, down toward the arid nation's border with Sudan.
Ghana long ago dammed the River Volta, Egypt the Nile, Zambia, Zimbabwe and Mozambique the Zambezi.
The prospect of secession by southern Sudan worries Egypt: it fears that a new political actor on the Nile might disturb the river's flow, Egypt's lifeline.
For example, significant cooling and strong dynamical effects after the Laki event and other high-latitude eruptions are believed to have caused decreased flow of the Nile River in Egypt and weakened African and Asian monsoons based on climate model simulations, with potentially very significant impacts on food and water supplies.
Balloon rides are a popular way to see the numerous ancient sites which line the banks of the River Nile at Luxor, in the south of Egypt, such as the temple of Karnak and the royal tombs in the Valley of the Kings.
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Across all of Africa the impact of human activity is clear - whether in the newly irrigated areas created by the waters of the Nile, turning huge areas of the desert around Egypt's lake Nasser green, or the urban sprawl of Dakar, across the Cap Vert peninsula in Senegal.
The Blue Nile originates in the country's Lake Tana and flows hundreds of miles north into Sudan and then Egypt before eventually flowing into the Mediterranean.
But Egypt, concerned to ensure the flow of Nile water, is agitated by the possibility of southern secession from Sudan's Muslim north.
Meanwhile, dozens of riot police and barriers surrounded the parliamentary building, but guards there allowed lawmakers into the building Monday, Egypt's state-run Nile TV reported.
But since Egypt, the biggest and most influential consumer of Nile water, is distracted by revolutionary upheaval at home, this may be changing.
Usually, he and Marchand dream up their thongs and wedges while floating down the Nile, but this year, because of the unrest in Egypt, they relocated to Brazil.
But the ancient rite, common in the Nile Valley and other parts of Africa, has remained particularly prevalent in Egypt.
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Dozens of relatives of those killed in Egypt's demonstrations gathered outside the court, state-run Nile TV reported.
Yet, according to the World Bank, it has provided a bulwark against flooding for buildings and crops, a huge expansion of farming and Nile navigation (lots of tourism) and enough electricity for the whole of Egypt all of which amounts to the equivalent each year of 2% of GDP in net benefits.
Egypt's meddling advances its interest of preventing the African nations from mounting a unified challenge to Egypt's colonial legacy of extraordinary rights to the waters of the Nile River which flows through all countries of the region.
Egypt's state-run Nile TV showed at least two members of the military police suffering injuries and being carried away from the front line of the clashes.
The pastoralists took refuge in the Sahel, Saharan highlands and Nile Valley, where they gave rise to numerous African cultures, including that of Pharaonic Egypt.
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