After 11 years of construction, the Aswan High Dam across the Nile River in Egypt is completed on July 21, 1970. More than two miles long at its crest, the massive $1 billion dam ended the cycle of flood and drought in the Nile River region, and exploited a tremendous source of renewable energy, but had a controversial environmental impact.

A dam was completed at Aswan, 500 miles south of Cairo, in 1902. The first Aswan dam provided valuable irrigation during droughts but could not hold back the annual flood of the mighty Nile River. In the 1950s, Egyptian leader Gamal Abdel Nasser envisioned building a new dam across the Nile, one large enough to end flooding and bring electric power to every corner of Egypt. He won United States and British financial backing, but in July 1956 both nations canceled the offer after learning of a secret Egyptian arms agreement with the USSR. In response, Nasser nationalized the British and French-owned Suez Canal, intending to use tolls to pay for his High Dam project. This act precipitated the Suez Canal Crisis, in which Israel, Britain and France attacked Egypt in a joint military operation. The Suez Canal was occupied, but Soviet, U.S., and U.N. forced Israel, Britain and France to withdraw, and the Suez Canal was left in Egyptian hands in 1957.

Soviet loans and proceeds from Suez Canal tolls allowed Nasser to begin work on the Aswan High Dam in 1960. Some 57 million cubic yards of earth and rock were used to build the dam, which has a mass 16 times that of the Great Pyramid at Giza. On July 21, 1970, the ambitious project was completed. President Nasser died of a heart attack in September 1970, before the dam was formally dedicated in 1971.

The giant reservoir created by the dam—300 miles long and 10 miles wide—was named Lake Nasser in his honor. The formation of Lake Nasser required the resettlement of 90,000 Egyptian peasants and Sudanese Nubian nomads, as well as the costly relocation of the ancient Egyptian temple complex of Abu Simbel, built in the 13th century B.C.

The Aswan High Dam brought the Nile’s devastating floods to an end, reclaimed more than 100,000 acres of desert land for cultivation, and made additional crops possible on some 800,000 other acres. The dam’s 12 giant Soviet-built turbines produce as much as 10 billion kilowatt-hours annually, providing a tremendous boost to the Egyptian economy and introducing 20th-century life into many villages. The water stored in Lake Nasser, several trillion cubic feet, is shared by Egypt and the Sudan and was crucial during the African drought years of 1984 to 1988.

Despite its successes, the Aswan High Dam has produced several negative side effects. Most costly is the gradual decrease in the fertility of agricultural lands in the Nile delta, which used to benefit from the millions of tons of silt deposited annually by the Nile floods. Another detriment to humans has been the spread of the disease schistosomiasis by snails that live in the irrigation system created by the dam. The reduction of waterborne nutrients flowing into the Mediterranean is suspected to be the cause of a decline in anchovy populations in the eastern Mediterranean. The end of flooding has sharply reduced the number of fish in the Nile, many of which were migratory. Lake Nasser, however, has been stocked with fish, and many species, including perch, thrive there.