Travel to Egypt today, and you might be surprised how sparsely populated and uninhabitable most of it is — just desert landscape on top of desert landscape. Except for the region around the Nile river. There is the birthplace of human civilization, the river in the middle of the desert that overflowed its banks nearly every year, depositing nutrient-rich soil perfect for lush plant and animal life, and later, human agriculture. But depending on the unpredictable ebbs and flows of the Nile was no way to live in the modern era, and Egypt decided on a dam to make the overflow predictable and measured.

On this day, July 21, in 1970, the Aswan High Dam, a water reservoir holding about four times the amount of water in the Hoover Dam, was completed. In addition to taking excess overflow of water in boon years and releasing it during droughts, the dam has served as a producer of hydroelectric power for the Nile region, where 95% of the population of Egypt resides.

The damming of the river has come with a price, however — the nutrient-rich soil renewed ever year by the river is now mostly stuck at the bottom of the dam, and as a result the quality of the soil around the Nile has worsened considerably. More than half of the land in the floodplain is rated medium to poor, and farmers have taken to importing fertilizer to make up the difference.