Across the bay, at a fish packing plant, fishermen had to wade ashore with their Nile perch in flat-bottomed boats, and heave the silvery catch up to a jetty that soon may be on dry land and out of reach entirely. Looking on, plant manager Ravee Ramanujam wondered about what's to come.

“Such a large body of water, dropping so fast,'' he said.

At 27,000 square miles, the size of Ireland, Victoria is the greatest of Africa's Great Lakes -- the biggest freshwater body after Lake Superior. And it has dropped fast, at least six feet in the past three years, and by as much as a half-inch a day this year before November rains stabilized things.

The outflow through two hydroelectric dams at Jinja is part of the problem -- a tiny part, says the Uganda government, or half the problem, say environmentalists. But much of what is happening to Victoria and other lakes across the heart of Africa is attributable to years of drought and rising temperatures, conditions that starve the lakes of inflowing water and evaporate more of the water they have.

An extreme example lies 1,500 miles northwest of here, deeper in the drought zone, where Lake Chad, once the world's sixth-largest, has shrunk to 2 percent of its 1960s size. And the African map abounds with other, less startling examples, from Lake Turkana in northern Kenya, getting half the inflow it once did, to the great Lake Tanganyika south of here, whose level dropped over five feet in five years.

“All these lakes are extremely sensitive to climate change,'' the U.N. Environment Program warned in a global water assessment two years ago.

Now, in a yet unpublished report obtained by The Associated Press, an international consulting firm advises the Ugandan government that supercomputer models of global-warming scenarios for Lake Victoria “raise alarming concerns'' about its future and that of the Nile River, which begins its 4,100-mile northward journey here at Jinja.

The report, by U.S.-based Water Resources and Energy Management International, says rising temperatures may evaporate up to half the lake's normal inflow from rainfall and rivers, with “severe consequences for the lake and its ability to meet the region's water resources needs.''

A further dramatic drop in Victoria's water levels might even turn off this spigot for the Nile, a lifeline for more than 100 million Egyptians, Sudanese and others.

“People talk about the snows of Kilimanjaro,'' said Aris P. Georgakakos, the study's chief author, speaking of that African mountain's melting glaciers. “We have something much bigger to worry about, and that's Lake Victoria.''

Each troubled lake is a complex story.

Lake Chad's near-disappearance, for example, stems in part from overuse of its source waters for irrigation. Deforestation around Lake Victoria, shared by Uganda, Kenya and Tanzania, makes the area a less efficient rain “catchment'' for the lake, and overfishing and pollution are damaging its $400-million-a-year fishing industry. Kenya's Rift Valley lakes, some just a few feet deep, have always fluctuated in size, even drying up with drought.

But African leaders say things are different this time, because long-term climate change may eclipse other factors.

“These cycles, when they've happened, they haven't happened under the circumstances pertaining now -- the global warming, overpopulation, degradation,'' said Maria Mutagamba, Uganda's water and environment minister.

African temperatures rose an average 1 degree Fahrenheit in the 20th century -- matching the global average -- and even more in the past few decades in such places as Lake Tanganyika, climatologists say. If greenhouse gases continue to build in the atmosphere, temperatures may be several degrees warmer by this century's end.

At Lake Victoria's receding shoreline, a place of scavenging storks, weedy expanses of water hyacinth, fishing boats derelict on dried lake bed, people see what's happening but don't understand why.

“In just a few years, the lake pulled back from there, maybe 60 meters (200 feet),'' said fisherman Patrick Sewagude, 24, pointing to old high-water marks at Ssese Beach, near Kampala, Uganda's capital.

Someone had planted a few rows of corn on the exposed lake bed. Grass was taking over elsewhere. “It's tough. The fish have gone way out. You pull up stones in your nets,'' Sewagude said.

Back in Jinja, 40 miles east of Kampala, researchers at the Lake Victoria Fisheries Organization said falling water levels are the latest blow to the dying biology of Lake Victoria, where pollution has helped kill off scores of unique species of tropical fish in recent decades. Now tilapia, once a prime food fish, are declining because their inshore breeding grounds are vanishing.

“People for many years haven't seen such a sudden change in the lake level,'' said the fisheries office's Richard Ogutu-Ohwayo, a biologist on the lake for 35 years. “Right now it's very difficult to say what will happen. It's a grim scenario, of worldwide climate change.''

Around the lake shore, everyone has his own theories.

“The water's too hot, and the fish are going deeper, beneath the nets,'' said Modi Kafeel Ahmed, a Jinja fish processor. But the lake has been overfished, too, he said. “If it goes like this another five years, the lake will be empty of fish.''

For 30 million people living in its basin, Lake Victoria is a vital source -- of livelihoods and food, of water, of transportation, of electric power.

Almost 200 miles across the lake from here, Tanzanian authorities have reduced water supplies to the city of Mwanza because an intake pipe was left high and dry. The same is happening in Uganda, where German engineer Erhard Schulte is pushing work crews to finish refitting Entebbe's city water plant, extending its intake pipe 1,000 feet farther out into the lake.

“The old Britisher who designed the original plant never expected the lake would drop this way,'' Schulte told a visitor.

Perhaps the worst impact is on power supplies. Tanzanian factories have shut down because the rivers powering hydroelectric dams, and replenishing Lake Victoria, are running dry. Kampala, a city of more than 1 million, has endured hours-long blackouts daily.

Uganda's two big hydro dams, side by side on the Victoria Nile, the lake's only outlet, are victims and -- some say -- prime suspects in the crisis.

In 2003, facing growing Ugandan demand for electricity, the Nalubaale and Kiira dams produced a peak 265 megawatts of power. In the process, their operators began overshooting long-standing formulas regulating flow of water out of the lake, an independent hydrologist later concluded.

That outside study, cited by environmentalists, contends 55 percent of the lake-level drop since 2003 is traceable to excessive outflow. But the dams' private operators and Ugandan officials strongly dispute that.

Paul Mubiru, Ugandan energy commissioner, says the dams have had a “negligible'' impact on Lake Victoria, and points to Lake Tanganyika's similar fall in levels -- with no dams involved.

Earlier this year, the operators announced they were reducing the dam outflows, “but our observations show that even with the reduced outflow, the water loss is still on the increase,'' Mutagamba, the water minister, told the AP.

Falling lake levels, meantime, mean lower “head'' pressure at the dams. Their output has dropped to 120 megawatts, pushing Uganda deeper into economic crisis.

It is such unanticipated ripple effects -- from abrupt environmental change -- that underlie the warnings worldwide about global warming. Scientists find another unexpected example in Lake Tanganyika, where they say warmer surface waters may be depleting fish stocks.

Many African lakes go unvisited by scientists, but what is known is troubling enough, says veteran researcher Robert E. Hecky, of Canada's University of Waterloo. “It is some of the most imperative data we have, that global climate change can be affecting these African water bodies,'' he said.

A “very comprehensive, very realistic'' study of Lake Victoria is needed, preferably conducted by U.N. specialists, said Frank Muramuzi, the head of Uganda's leading environmental organization.

“Businesses are standing still, not working. Fishermen can't get enough fish. We do not have enough water supplies,'' Muramuzi said. “Rains alone won't bring back the lake levels, because there would still be climate change, a lot of heat, evaporation. It's reached a point where people don't know what to do.''