On July 21, 1970, engineers completed the Aswan Dam in southern Egypt. The Aswan Dam was an enormous project, lasting more than 10 years and costing more than a billion dollars. At the time of its construction, it was the largest rockfill dam. Abbas Sharaky, a water resources professor at Cairo University, said of the dam to the Associated Press, “it is the greatest Egyptian project since the time of the pharaohs.”

While the dam provided many benefits to the region, it also negatively impacted the environment and the people displaced by construction, generating lasting controversy in the area.

The Aswan Dam controls the flow of the Nile River, which protects people living near the banks of the Nile from both floods and droughts. The constant, regulated flow of water helps farmers irrigate their crops all year. The dam also improves navigation on the Nile and provides hydroelectric power. Its 12 turbines generate 10 billion kilowatt-hours of electricity, which is used in homes, schools, businesses and hospitals throughout Egypt. When the dam was built, the power it generated supplied nearly half of Egypt’s needs.

For some Egyptians, whose homes and croplands would flood for at least one-third of the year before the dam, the benefits are significant. Before the dam improved flood management, some residents like Yassin Saeed had to use felucca sailboats to reach their crops.

The electricity generated by the dam meant that many Egyptians had electricity for the first time, which also brought jobs. The dam’s construction also drew support of those who saw it as a source of Egyptian pride.

Before the construction of the current Aswan Dam, also known as the Aswan High Dam, the British built the Aswan Low Dam in 1902 to control flooding. Following the 1952 Egyptian Revolution, Egyptian President Gamal Abdel Nasser prioritized building a larger dam to aid industrialization in the region and reduce dependence on other nations. At least 25,000 Egyptian engineers and workers built the new dam. At first, the United States, Britain and the World Bank planned to fund the Aswan High Dam, hoping to reduce Soviet influence in the region. However, they withdrew funding after discovering that the Egyptians had an arms agreement with Czechoslovakia. Subsequently, the Soviet Union stepped in to fund the project.

The Aswan Dam created a huge reservoir—called Lake Nasser by the Egyptians and Lake Nubia by the Sudanese—which is one of the largest human-made lakes in the world. But the creation of the lake and the expansion of the Nile behind the dam displaced more than 50,000 people in Egypt and Sudan. Many of these displaced people were Nubians, an ethnic group indigenous to the area and connected to one of Africa’s oldest civilizations. The lake flooded their villages, and the Egyptian government moved them from their homelands to Kawm Umbu (Kom-Ombo) Valley, north of Aswan.

The Egyptian government promised new, modern homes and farmland for those displaced, but reality fell short of these promises. In some cases, no homes were built, but those the government did construct were cramped and lacked electricity and running water. People also waited years to receive farmland that turned out to be too dry to use for farming. Many found the transition difficult and became impoverished in this new environment due to the trauma of forced relocation and inadequate support from the Egyptian government.

In recent years, the Egyptian government has tried to compensate Nubians and the descendants of people displaced by the dam’s construction. Nubians have received reparations in the form of cash, housing or land ownership. But many dream of returning to their homeland. Today, young activists are drawing attention to the cause.

In addition to affecting the local population, the dam also changed the area’s ecology. The Nile’s historic annual floods brought ample flow of nutrients to the soil, which nourished crops. This changed after the altered flow restricted distribution of nutrient-rich sediment. Farmers have come to rely on artificial fertilizer, which is expensive and often inadequate. Some evidence even indicates that fluctuations in water levels of Lake Nasser can change water pressure in pores of rocks under the reservoir, which may have increased seismic activity in the area.

The dam also drowned priceless archaeological sites. This attracted international attention, which led to a campaign from UNESCO to save threatened ancient artifacts. The Egyptian government famously relocated features from one of these sites—colossal monuments of Pharaoh Ramses II—to a nearby hill before the site was flooded.