There is a science-fiction eeriness about it, like a lake on Jupiter or Mars. Fierce blast-furnace winds, 115-degree heat. A white-hot haze hangs over the choppy blue waves like steam on a vat. Nothing to see but sand and rock on the shore, home of jackals, poisonous snakes, and scorpions. The few primitive wooden fishing boats are widely scattered, lonely and isolated.
Small wonder they call the fishermen arraqa - ''those who sweat for a living.''
This is Lake Nasser, created 20 years ago when the Aswan High Dam, built under Soviet guidance and finance, began storing water, ending the Nile's periodic floods. Egypt's late President Gamal Abdel Nasser himself called it ''the largest lake ever shaped by humankind'' and predicted it would be ''an everlasting source of prosperity.''
Today, the 1,640-foot-long High Dam Lake no longer officially bears his name (and the southern third in Sudan is called Lake Nubia). Americans are rebuilding the Soviet turbines for $100 million. A 210-foot-high concrete lotus flower built to symbolize Soviet-Egyptian friendship has instead become a monument to the shifting tides of politics. Most people, if they think of the Aswan Dam at all, think of ecological backlash.
Yet this could be the year when President Nasser and the dam's other architects are vindicated at last. Africa faces the worst drought in living memory and the Nile's sources in the Ethiopian highlands and the lake regions of Uganda and Tanzania have been severely affected. The river's flood this summer was expected to fall to the lowest levels this century. Lake Nasser is predicted to drop to about 535 feet, the lowest level since it was filled.
Without this vast reservoir, Egypt, too, would be facing drought and famine on a biblical scale this year. Instead, its big problem is waterlogging. The underground water table of the Nile valley and delta, despite massive World Bank-funded drainage efforts, keeps rising. To blame are a failure to install a good drainage network in the 1960s and peasants' overuse of irrigation water.
Given Egypt's need to double or triple its land usage to feed 47 million people on just 5.7 million irrigated acres, few now dispute the need for the Aswan Dam. In the old days, whether the Nile's flood was high or low, there was just one harvest.
The dam's biggest environmental problem was predicted from the start: high rates of evaporation from scorching heat and high summer winds. The Nile is getting a little saltier. Algae produced in the lake a few years ago clogged Cairo's filter system, turning tap water muddy. The riverbed is being scoured, the Mediterranean coast eroded.
Ethiopian silt, no longer enriching the valley's soil, could fill up the lake in 500 years.
The latest problem is that Lake Nasser's sheer weight (a capacity of 164 billion cubic meters of water) may have triggered two small earthquakes in 1981 along the Kalabsha geological fault, which runs under the lake about 40 miles south of Aswan. In July there were two smaller tremors 250 miles northeast on the Red Sea. Houses were shaken in Aswan.
Unlike some of the clifflike concrete American dams, where a breach can release a wall of water, the Aswan High Dam is considered unusually safe, because it is nearly a kilometer thick at its base. It looks less like a conventional dam than a gigantic, squashed-down man-made mountain of clay capped by rock and impacted sand. It is sometimes called ''Nasser's pyramid.''
With Sudan torn by civil war, the dam's location within Egypt's borders also takes on new strategic value. Sudan's southern Christians and animists, rebelling against an increasingly fundamentalist Muslim north, recently drove out French engineers who had excavated about two-thirds of the 217-mile Jonglei Canal, on which both Egypt and Sudan were banking for more irrigation water. It would increase the White Nile's flood by channeling the river around Sudan's great Sudd Swamp. Also driven from the Sudd, where large untapped oil deposits have been found, were Chevron Oil Company workers who feared rebelling Nuer and Dinka tribesmen.
On Lake Nasser itself, one gets the feeling of being in the eye of a storm. A big question remains, after the dam's storage, irrigation, and power benefits: What is Egypt to do with the lake now that it exists? When the lake started to fill in 1964, displacing the formerly riverine Nubian population of more than 100,000, Egypt hoped someday to resettle about twice that number on the two-thirds of the lake within its borders through fishing, tourism, and a green, irrigated belt of villages.
It takes time. Aside from 180,000 people in Aswan, about a thousand settlers at Abu Simbil, plus some Nubians trying to farm along the nearby shore and a few government installations, nobody lives on the lake. There is a shifting population of fishermen, estimated at from 3,000 to 10,000.
Lake Nasser has been too windy for the Nile's traditional sailboats, or fellucas. A primitive fleet of about 2,000 15-foot wooden boats with oars or small motors has managed to produce a yearly catch of about 25,000 tons of fish, a fifth of Egypt's total production.
About 100,000 tourists a year take the relays of daily flights from Aswan to Abu Simbil, down the lake by the Sudanese border, to view the great temples of Ramses II and Nefertari.
The harshness of the lake's environment was dramatized last year when a ferry traveling from Aswan to Wadi Halfa caught fire with 600 passengers aboard. Half were lost, but survivors who swam to shore told harrowing tales of crocodiles and scorpions.
A big role in helping to tame such a hostile setting has been played by CARE, the international relief organization. Working with Egyptian fishermen's societies, CARE is building 88 shelters and providing pumps, insecticides, saplings, garden seeds, and first-aid kits, plus a new medical boat.
Japanese experts say 80 percent of Lake Nasser's water is still empty of fish , and they recommend stocking the lake with silver carp. A Japanese blueprint, called ''Expected Development by 2000,'' calls for ice-water fish storage and such emergency services for the fishermen as a radio network and helicopter rescue.
Already partly achieved are a nursery, new fishing harbor, a pilot farming village, a modern Japanese-run fisheries center, and new medical boats. Americans may soon agree to finish a paved road that now reaches down about halfway between Aswan and Abu Simbil on the lake's western shore. The Japanese see no reason why the fish catch can't be increased to 80,000 tons a year.
Slowly Lake Nasser could come to life with fishing, farming, mining, and tourism. In the meantime, its sheer empty space and silence are awesome, a world of sun and stars, all that water and heat and wind.