Earlier this month, the foreign ministers of Sudan, Egypt and Ethiopia reached agreement on basic principles for managing what will be Africa’s largest hydroelectric dam, which is now under construction on the Blue Nile near the Ethiopian-Sudanese border.

While the unilateral building of big dams is often a trigger for conflict in international river basins, the Grand Ethiopian Renaissance Dam has the potential to forge much-needed cooperation and some win-win opportunities for those three Nile Basin countries.

Although its details have yet to be disclosed, the agreement would appear to open pathways to shared economic benefits from the Nile’s waters as well as to greater flexibility and resilience in times of drought.

But it also creates conditions for the resurrection of an engineering scheme in South Sudan that could harm one of the largest and most wildlife-rich wetlands in the world.

A Complicated History

The Nile Basin now has 11 countries within it, but the two most downstream – Egypt and Sudan – have staked claims to the entire river’s flow.

The Blue Nile originates in the highlands of Ethiopia. At Sudan’s capital of Khartoum, it joins the White Nile, which begins around Lake Victoria.   The two then flow together as one Nile north into Egypt and out to the Mediterranean Sea.

Egypt has long worried – with good reason – that upstream water development in Ethiopia would cut off some of its lifeline. Egyptian leaders from Anwar Sadat to Mohammed Morsi have warned of going to war over water if the nation’s supplies became threatened.

A stumbling block to equitable water-sharing in the basin is a 1959 treaty between Egypt and Sudan that allocated the entire flow of the Nile to just those two countries, even though 84 percent of the river’s flow originates in Ethiopia. Not surprisingly, Ethiopia never recognized the legitimacy of that agreement. But for decades it had neither the political stability nor the financial means to undertake the kind of large-scale water development that would challenge Egypt’s historic claims to the river.

That situation changed in 2011. As Egypt was preoccupied with the Arab Spring and the fall of the Mubarak government, Ethiopia announced that it would begin construction of a massive dam on the Blue Nile near the border with Sudan.

Now about 30 percent complete, the 145-meter-high Grand Ethiopian Renaissance Dam (GERD) is expected to cost some $4.8 billion and be completed in 2017. (If experience with other big dams holds true, it will cost more and take longer than these estimates.) The GERD would have the capacity to generate more than twice as much hydroelectric power as Egypt’s Aswan Dam, and more than Ethiopia itself can use for some time. The sale of power to neighboring Sudan is therefore critical to make the project financially viable. (Some experts say that Ethiopia has grossly overestimated the amount of power the dam will actually produce with the river flows available.)

The GERD would also be able to store more than a year’s worth of the Nile’s flow. Filling the reservoir, especially if done during dry years, would almost certainly reduce flows into Egypt.

But if equitable water-sharing accompanies rules for filling and operating the dam, the three countries could find themselves with more total water to share. That’s because evaporation rates are lower at the Grand Renaissance location than at Aswan. So storing more Nile water at the GERD, and less at Aswan, should add to the total water available for energy and irrigation among the three countries.

Moreover, since hydropower runs water through turbines but does not “consume” it, Ethiopia’s decision to pursue a more hydroelectric-centered approach to economic development, rather than one based heavily on highly water-consumptive irrigated agriculture, actually benefits Egypt. Less water consumption upstream means more is available to flow downstream into Egypt.

As Nile Basin expert Dale Whittington of the University of North Carolina at Chapel Hill and his colleagues write in the journal Water Policy, the Grand Renaissance Dam “is Ethiopia’s first big step on a hydropower water development path for the Blue Nile, and Egypt should encourage Ethiopia to choose this option.”

But the Nile flows through Sudan first, and with a reliable supply of irrigation water from the GERD, Sudan’s fertile lands could boost the nation’s food production and exports. Because Sudan has never used its full allotment of the Nile under the 1959 treaty, Egypt has actually been using part of Sudan’s share in addition to its own. An expansion of irrigated agriculture in Sudan could reduce flows into Egypt.

Greatly complicating the situation, when Sudan divided into two nations, there was no clarification of how Sudan and South Sudan would share the Nile’s water. Seeing an opportunity, Egypt has signed an agreement with South Sudan to cooperate in the development of the new nation’s water sources – presumably in a way that would yield more water for Egypt.

Enter the Sudd Swamps

A leading contender for the development of South Sudan’s water is the resurrection of an engineering scheme known as the Jonglei Canal. Designed decades ago, it would divert the White Nile away from the vast Sudd Swamps, a watery wilderness that supports a treasure trove of wildlife –including elephant, gazelle, hippopotamus, zebra and several varieties of antelope.

The Sudd wetlands are also home to millions of migratory birds during the course of the year, with the glossy ibis population alone numbering some 1.7 million during the dry season.

A number of Nilotic tribes — including the Dinkas, Nuer and Shilluk – also thrive in the Sudd. With populations collectively numbering 200,000-400,000, they key their lives of pastoralism, fishing and agriculture to the seasonal cycle of flooding and the rich biodiversity of the region.

But the very vastness that makes the Sudd such an important and unique habitat also makes it a source of huge evaporation losses. The goal of the Jonglei Project — which was 70 percent complete when the Sudanese civil war broke out in 1983 – was to capture about 4 billion cubic meters of water a year (just under 5 percent of the Nile’s total annual flow) that would otherwise evaporate.

The ecological and cultural harms from the project were never fully examined, but could include a drying out of grazing lands, a drop in groundwater levels, the collapse of fisheries and the loss of critical habitat for wildlife.

In 2006, the Sudd was designated a Ramsar Wetland of International Importance, shining a spotlight on the Sudd’s importance to global conservation.

But in its quest for water security, Egypt now eyes the completion of the Jonglei irrigation scheme as a priority.

So while on balance the recently signed agreement between the three Nile nations shows promise for easing tensions and sharing the river’s benefits more equitably, the new risks to the Sudd are real and warrant consideration at the negotiating table.

Through investments in irrigation efficiency, smarter water management, regional trade and sound economic development, the three nations can benefit from greater cooperation over the Nile without sacrificing one of the region’s – and planet’s – great wetland wildernesses.

Originally published at National Geographic Newswatch.