To walk the Forgue dairy farm is to step into a picture postcard. The view from the pastures is of maples and oaks ramping up their fall color explosion and the Green Mountains rising in the blue-gray distance. Across a field of heather and through a stand of birches lies Lake Champlain, the nation's sixth-largest freshwater lake.

But few folks up here put more than a toe in those once-pristine waters this summer. A green algae goo covered the surface.

"I grew up with that lake as my back yard," said Travis Forgue, 31, an organic dairy farmer who has become an environmental leader in this far northwestern corner of the state. "Now we don't let our kids swim in the lake. That's very sad to me."

Poor dairy farming practices and ever-expanding development along its shores are threatening the health of Lake Champlain, a 120-mile-long lake formed by glaciers and long a symbol of this mountain state's environmental commitment. Phosphorus from cow manure and runoff from homes, businesses and paved roads has poured into rivers and streams, and into the lake itself for many years. Now tons of it sit on the lake floor, and when the summer sun beats down, the phosphorus acts as a sort of steroid for algae.

The result is giant algae blooms.

The cyanobacteria blooms have afflicted the northern end of the lake for a decade now, sickening some adults and claiming the lives of dogs unfortunate enough to plunge in for a summer swim. This past summer produced the largest bloom yet, a thick blanket of green scum that covered the three mile width of the Missisquoi Bay and leaked south. Floating clouds of foam clogged picturesque passages in the Champlain Islands, a necklace of small isles and towns.

The southern and central regions of the lake still remain algae-bloom free.

"If something isn't done dramatically and quickly, we're putting this entire lake in danger," said Jeffrey Wennberg, commissioner of the state's Department of Environmental Conservation. "We are very much running out of time."

On the Canadian border of the lake, the algae bloom forced several campgrounds on Missisquoi Bay to all but shutter their businesses in mid-August. "The stink was miserable," said Gino Tutino, the white-haired owner of Domaine Samuel de Champlain, a hotel and restaurant just half a mile north of the border. "The flies and mosquitoes were attracted to it, and it will not surprise you that a lot of guests were not amused."

More than 200,000 Vermonters -- about one-third of the state's population -- draw their drinking water from the lake and watershed. The lake's shores, ringed with red-rock cliffs, sandy beaches and the Adirondack peaks, draw hundreds of thousands of visitors, who spend tens of millions of dollars.

Some of the lake's ills are of distant origin, such as the mercury that arrives via the jet stream from coal-burning power plants in the Midwest. But more problems are homemade -- particularly in Vermont, a state with a national reputation for environmental stewardship. The Green Mountain State contributes at least 60 percent -- and probably much more -- of the phosphorus that flows into the lake. And two dozen Vermont streams in the Lake Champlain watershed fail minimum clean-water standards. The New York side of the lake is bordered primarily by the sparsely inhabited Adirondacks State Park.

"If I was a New Yorker or a Quebecois, I'd be outraged by Vermont's performance," said Chris Killian of the Conservation Law Foundation. "The state has not begun to live up to its 'green' reputation."

The growing problem has forced state officials to reckon with dairy farmers, who, even as their herds diminish, loom large in Vermont's cultural iconography. Years ago, Vermont enacted a "best practices" guide, which encouraged dairy farmers to build manure pits, dig trenches and plant trees between their pastures and nearby rivers and streams. Farmers were asked not to spray manure to fertilize their fields in the winter, when it more easily runs off.

But the guidelines were voluntary, and virtually no money was set aside for inspections. When farmers ignored the guidelines, many neighbors were reluctant to blow the whistle.

Nor have Vermont officials forced farmers, even of the larger corporate variety, to apply for a Clean Water Permit, as it requires of certain large businesses. Canada, by contrast, has required its farmers to comply with clean water rules.

"It's a double whammy -- we have poor farming practices, and we're bringing more and more people into the watershed," said Mary Watzin, director of the Rubenstein Ecosystem Science Laboratory at the University of Vermont. "Even if we act now, it's probably going to take a couple of decades for the lake to clean itself."

Watzin added that dairy farmers often operate on razor-thin profit margins. And Vermont, particularly under former governor Howard Dean (D), tended to underfund agricultural environment programs, forcing conscientious farmers to scrimp to establish stream buffers. Dean's administration also let more than 1,700 wastewater permits expire without reinspections.

Now a zephyr or two of change can be felt. Gov. Jim Douglas (R) was elected two years ago as the algae blooms grew in size and scope. He agreed to bring forward deadlines for reducing phosphates in the lake. And he committed to putting in millions more dollars to help farmers clean up their pastures. But so far, the programs have more farmers than money.

"A lot of the farmers can't afford to do it themselves," said state Sen. Donald Collins (D), who represents a district in northern Vermont and who grew up on a dairy farm. "We've got a lot of farmers signed up, but we don't have the money."

For the first time, the state will require that farmers comply with regulations requiring stream buffers and other remedies. "We realized that if we wanted to remove the amount of phosphorus that we needed from the lake, we could no longer make it voluntary," said Wennberg, the state environmental commissioner.

Killian of the Conservation Law Foundation takes such promises with a pound or two of salt. He says the state still falls short of providing the needed dollars. And he says the Douglas administration remains too tolerant of the large developments whose parking lots and acres-large roofs produce rain runoff that washes tons of phosphates into the lake. His organization recently sued successfully to stop a large development in South Burlington.

"We are doing an excellent job of documenting the death of the lake," he said. "Now we need to see some real money poured in to save it."

There's no disputing the hold the 435-square-mile body of water has on the imagination of many Vermonters. Revolutionary War battleships lie in its 400-foot depths, and six-foot-long sturgeon, a fish that can live more than 100 years, still breed in its tributaries.

Roger Lanoue, a red-haired son of French Canadian farmers, sat by a slate-gray beach and watched the wind ripple the surface of Missisquoi Bay a few days ago. Only weeks earlier the waves had pitched up a green scum.

"Our lake is in bad shape, eh?" He shrugged. "What do you expect? We've been hurting her for years and years before she turned. She won't clean itself up overnight."

Vermont is trying to clean up Lake Champlain by reducing the pollutants from dairy farms and development that flood into its waters. Toxic algae blooms form in hot weather, making the water unsafe. Gino Tutino said his hotel on Lake Champlain was almost shut down in the hot weather because algae blooms had such an unpleasant odor.