MAUN, Botswana -- The Boro River is a narrow thread of blue twisting languidly through the lower reaches of the great Okavango swamps. Golden reed shafts arch over its shallow banks as white waterlilies bob in the radiant sun.
"Doesn't look big enough to stir up so much trouble, does it?" asked Isaac Tudor, an adviser to the chief of the BaTawana tribe.
It doesn't take much water to start trouble in a country dominated by the world's fourth-largest desert, the Kalahari. A population of 1.3 million -- smaller than Philadelphia's -- is spread across an arid landscape the size of France.
The Boro has become the focus of a growing international dispute pitting the BaTawana tribe and major environmental groups against the Botswana government and the powerful De Beers mining conglomerate. At issue is a scheme to dredge the river and extract precious water from the fragile, game-rich swamps.
The Okavango Delta, a sprawling network of loamy islands and oozing bogs, is the largest inland delta in the world, bigger than New Jersey and home to countless hippos, crocodiles, lions and zebras. It sustains 92 species of fish, 400 kinds of birds and more than 100 species of mammals, including a major part of what is probably the largest elephant herd in Africa.
The Okavango is not only one of Africa's last pristine wildernesses -- what environmentalists call "a complete ecosystem" -- but also Botswana's top tourist attraction and the thirsty nation's prime potential source of water.
The government's plan to tap some of that water has environmentalists and tour operators sounding a global red alert, both because of the threat it poses to the Okavango and because they believe the plan is vague and ill-conceived.
Greenpeace has threatened to parody De Beers' famous "Diamonds are forever" slogan with a "Diamonds are for death" campaign, urging consumers to boycott the gems unless dredging is stopped. It's a threat Botswana must take seriously: Diamonds constitute about 80 percent of its economy.
"The Okavango Delta is one of the world's great natural treasures," said ecologist Karen Ross-Greer. "Any development should be studied thoroughly and measured against the potential irreparable effects. Once it's broken, it can't be fixed."
Heavy equipment has already arrived in Maun, with dredging set to begin. There are signs Botswana might postpone the 18-month project, but environmentalists are quickening their efforts.
Greenpeace accepted a government invitation to send a fact-finding delegation and asked for a suspension of the project in the meantime.
"It remains to be seen whether we can stop them in time," said Hazel Wilmot, a produce dealer involved in anti-dredging efforts. "I think we can."
The environmentalists' case is strongly supported by BaTawanatribal leaders, who carry considerable clout in this democratic nation. Chief Mathiba Moremi complains the BaTawana were not adequately consulted about the project.
Botswana's top minister for water and minerals, Archie Mogwe, has tried to woo the BaTawana. But John Benn, a former game warden, says Mr. Mogwe won't be successful.
"There are people here with memories longer than those in the government who are proposing this scheme," Mr. Benn said. "You know, this is not the first time they have tried to dredge the Okavango."
In 1938, laborers hand-dredged the smaller Gomoti River and then sat back to await the blessed flow. Instead, the Gomoti dried up.
In 1942, the Thaoge River was hand-dredged. The next year, it dried up.
And in 1973, a few miles of the lower Boro were dredged. It did not dry up, but its neighbor, the Santantadibe River, did.
Mr. Tudor says outsiders do not understand the swamp, and MrBenn agrees.
"This is the Okavango Delta, not the English Midlands. It is unique. You know that under us, not very far, are the sands of the Kalahari. The Okavango is like a miracle hanging on to the edge of the desert."
During the rainy season, the Okavango River pours furiously out of the highlands of southern Angola. Two parallel geological faults disperse the flow into a massive freshwater flood plain far from any sea -- an inland delta.
The first of the floodwaters cross into northern Botswana in January. Not until June do they emerge from the delta's southern rim, mostly through the Boro River.
The Lower Boro River Improvement Scheme calls for dredging 25 miles of the river, beginning at its mouth near Maun.
New roads would carry mobile dredgers as they carved a canal 2 yards deep through the shallow river. Earthen walls about a yard high would rise along each bank to retain most of the water from surroundingmarshes that have depended on it.
If the scheme worked, an estimated 50 million cubic meters of additional water would be channeled out of the Okavango each flood season, increasing by 17 percent the flow past Maun. Two new dams would hold it downstream.
Exactly what harm all this might cause is uncertain, mainly because of the quirky, labyrinthine nature of the delta, whose rivers suddenly dry up or spring to life after unpredictable seismic shifts.
Even the government's own environmental study acknowledges "certain adverse environmental impacts" on what it called a "partly degraded area" of the Okavango.
In a letter to the Botswana government, Ian MacPhail of the International Fund for Animal Welfare said that risking the destruction of the Okavango for this project would be "like demolishing Chartres Cathedral to grow potatoes on the site."
Botswana's top opposition leader, M. K. Mpho, who is based in the Okavango region, is also critical. "It will mean ending the life of the people of this country," he said. "The swamps will become a desert."
The most puzzling question, environmentalists say, is: Who really needs this extra water?
Until December, the government said much of it was needed to supply the huge Orapa diamond mining complex co-owned by De Beers and the Botswana government.
"Once Orapa got involved, a lot of people gave up," said one environmentalist. "In this country, what Orapa wants, Orapa gets."
But when Greenpeace threatened a boycott in December, De Beers suddenly disavowed the project.
The government now says the beneficiary is the village of Maun.
The small, dusty settlement of 25,000 is the administrative capital of northwest Botswana, home of BaTawana tribal leaders and main hub for safaris into the Okavango. It is also growing rapidly.
But residents and ecologists believe Maun doesn't need the water.
Why then has the government so stubbornly pushed the dredging?
Some believe that despite De Beers' denials, the water is still destined for Orapa. The diamond giant, they say, wants the water without the bad publicity and is willing to let the government take all the heat now while quietly taking the water later.