A war of words over control of the Nile has broken out between Egypt, which sees the river as its lifeblood, and countries upstream complaining they are denied a fair share of the river's water.
Presidents and officials from half a dozen countries have been crisscrossing Africa holding talks in the latest escalation of a decades-old dispute.
The Nile Waters Agreement, which still holds today, guarantees Egypt 55.5 billion cubic meters of the Nile's 84 billion total flow. Sudan gets the rest.
But the remotest headstream of the Nile rises 4,145 miles to the south, in Burundi's Ruvyironza River.
Its myriad tributaries drain a basin the size of the Amazon rainforest across 10 countries – the Democratic Republic of Congo, Tanzania, Burundi, Rwanda, Uganda, Kenya, Ethiopia, Eritrea, Sudan, and Egypt. Under the deal, and another reaffirming its principles in 1959, those last two have final say on projects affecting the Nile's flow. None of the others may tap into the river's bounty – for irrigation, for example – unless Cairo and Khartoum agree, and without that, upstream nations have struggled to access international finance to fund such projects.
"No donor or bank is going to agree to give money for a dam or an irrigation scheme if they know it's illegal in international law and does not have the backing of all the Nile nations, especially Egypt," says Salif Diop, an expert in international water conflicts at the United Nations Environment Program in Nairobi.
'Upstream' Africa wants to rewrite water rules
Now, the "upstream" nations, facing droughts and booming water demand, appear to have run out of patience. In late May, in Uganda's capital, Kampala, five of them inked a new Comprehensive Framework Agreement effectively setting the ball rolling to rip up the rule book.
Egypt, and Sudan have so far refused to sign up and the go-it-alone pact has strained Nile nations' relations. Cairo went on a diplomatic offensive.
Kenya's prime minister, Raila Odinga, flew in for talks with his Egyptian counterpart, Ahmed Nazif. Congo's president, Joseph Kabila, at the same time met with Egyptian President Hosni Mubarak. Burundi's leader, Pierre Nkurunziza, is soon expected to follow suit.
Cairo sees protecting its control over the Nile – which provides 95 percent of Egypt's water supplies – as a matter of national security. It is impossible to say how much water they would lose if dams and irrigation schemes starting blocking the Nile farther upstream, because that depends on the number and scale. Any interruption of its flow will, however, affect a huge proportion of its 85 million citizens, and the ribbon of industrial agriculture hugging the banks of the Nile as it snakes through Egypt's center.
'All faced with climate change'
But at least 200 million people farther south live across the Nile's total basin – a population that is expected to double within 50 years.
"Everyone knows we are all faced with the realities of climate change," said Stanislas Kamanzi, Rwanda's minister for environment and lands. "Rwanda is one of the most vulnerable countries, 80 percent of our agriculture relies on rain-fed irrigation, and we can no longer predict that we will receive regular rainfall, so we can't predict our crop production. We need to use the resources in our waterways and lakes, and these are clearly in the Nile Basin."
Rwanda, Uganda, and Ethiopia, whose economies are expanding as memories of civil conflict a decade ago fade and investors flock in, are all keen to exploit opportunities for commercial farming. But that needs water, and still the rivers that lead to the Nile, or the lakes that feed it, are the best source of untapped irrigation.
'China factor' crucial
Four-fifths of the water in the River Nile flows from the Ethiopian highlands into the Blue Nile, which joins with the relatively meager White Nile at Khartoum in Sudan. "Ethiopia knows it has the lion's share of the water that ends up in the Nile," Professor Swain says. "It has shown recently that it is not prepared to wait for basin-wide agreements to go ahead with large scale projects. What's changed to give them that confidence? China."
The "China factor" has been a crucial development which may soon force a final agreement. "Egypt, in their hearts, have always known that they are in a difficult position," says Swain. "But in the past they have been able to fall back on the influence they have had with the West to maintain the status quo. China listens less to that kind of diplomacy."
Beijing is already heavily invested in major infrastructure projects in Ethiopia – including a hydroelectric dam across one of the tributaries of the Blue Nile.
Egypt has acquiesced to this dam – and others like it in Uganda and Sudan – because hydroelectric schemes at least return the water into the Nile system. Not so irrigation projects.
"Egypt will delay as long as it can, but it cannot reasonably maintain [its historic] position for much longer," says Swain.