The River Nile has dozens of tributaries, down to the tiniest streams and rivulets. But the largest of them all is the Blue Nile, which flows from Ethiopia’s Lake Tana and joins the White Nile in Sudan, where it contributes about 85 percent of the water that makes up the main Nile. It’s also crucial to almost every aspect of life in Ethiopia; some 32 percent of the country lies in the Nile Basin and about forty percent of the population lives there. The Blue Nile is facing serious threats. Deforestation, overgrazing and erosion from agriculture are causing the river to silt up dangerously, adding to the threat of flooding in downstream countries. In addition, Ethiopia’s rapidly growing population is straining the available water.