The reservoir behind the largest hydropower plant in Africa has begun filling. Under construction since 2011, the Grand Ethiopian Renaissance Dam (GERD) is 1.1 miles long, 509 feet tall, and spans the Blue Nile River in Ethiopia.

The GERD reservoir is in a deep gorge, so its surface area is relatively small compared to its volume. This means less water will be lost to evaporation than in desert reservoirs. The lake’s capacity is about twice the volume of Lake Mead.

Including the Aswan High Dam in Egypt, which forms Lake Nasser and has the capacity of four times the volume of Lake Mead, two of the world’s largest dams are now on the Nile River system, in two different countries.

The first phase of GERD reservoir filling began in summer 2020. The curved shape southwest of the main dam is referred to as the Saddle Dam, and the reservoir reached it for the first time in 2022.

Landsat imagery may make it look like the lake is filling at a rapid pace, but filling the reservoir is still a gradual process. Filling too quickly could lead to hydrologic water shortages downstream, especially if a drought hits at the time.