Ethiopia has been at loggerheads with downstream neighbors Egypt and Sudan for years over a $4.8 billion mega-dam it’s building on the Nile River. Now the standoff is coming to a head as the Grand Ethiopian Renaissance Dam moves toward completion and the three nations wrangle over how quickly the 74 billion cubic-meter (2.6 trillion cubic-foot) reservoir behind the dam wall gets filled.

1. Why is the dam so significant?

The Nile is the most important source of fresh water in a largely arid region that is very vulnerable to drought and climate change and is experiencing rapid population growth. Egypt relies on the 4,000-mile-long river for as much as 97% of its supply, much of eastern Sudan’s population depends on it for survival, and Ethiopia is counting on a 6,000-megawatt hydropower plant on its new dam to boost the nation’s electricity supply by 150%.

2. What’s the issue with filling the reservoir?

Ethiopia had talked about closing the dam’s gates and filling the reservoir in two to three years, but now says it’s willing to extend the process to as long as seven years, starting in the current rainy season. Egypt has asked for the process to be drawn out over about 15 years so that the effect on water flow is more gradual and to allow for the impact of droughts. Tensions spiked in mid-July after satellite images showed water building up behind the dam wall and initial reports suggested the gates had been closed. Ethiopian officials subsequently said heavy rains had resulted in “natural pooling.”

3. Can the three sides reach an accord?

Mediation efforts that have drawn in the U.S., United Nations Security Council and African Union failed to yield a compromise. Ethiopia argued that it wasn’t obliged to negotiate with anyone, even as it participated in the talks. And Egypt has warned all options are on the table should the dam be filled unilaterally but has held back on threatening military action.