Waterways across the upper Midwest are increasingly plagued with ugly, smelly and potentially deadly blue-green algae, bloomed by drought and fertilizer runoffs from farm fields, that's killed dozens of dogs and sickened many people.

Aquatic biologists say it's a problem that falls somewhere between a human health concern and a nuisance, but will eventually lead to more human poisoning. State officials are telling people who live on algae-covered lakes to close their windows, stop taking walks along the picturesque shorelines and keep their dogs from drinking the rank water.

Peggy McAloon, 62, lives on Wisconsin's Tainter Lake and calls the algae blooms the "cockroach on the water."

"It is like living in the sewer for three weeks. You gag. You cannot go outside," she said. "We have pictures of squirrels that are dead underneath the scum and fish that are dead. ... It has gotten out of control because of the nutrient loads we as humans are adding to the waters."

Blue-green algae are common in waters but not every lake develops serious problems until plentiful "man-induced" nutrients like phosphorous arrive, said Jim Vennie, a Wisconsin Department of Natural Resources expert. The toxins released by the algae can be deadly. Symptoms include rash, hives, runny nose, irritated eyes and throat irritation.

No people have died in the U.S. from the algae's toxins, according to Wayne Carmichael, a retired aquatic biologist and toxicology professor in Oregon.

Many, however, have gotten sick: "Sooner or later, we are going to have more acute human poisoning," Carmichael said.

The scum has killed dozens of dogs over the years — including at least four in Oregon, three in Wisconsin and one in Minnesota this summer. Wisconsin wildlife experts are warning duck hunters with dogs to be extra cautious this fall. "If the water is pea-soup green, be sure to have clean water along to wash the dog off," Vennie said. "Don't let it drink the water."

Fewer than 100 lakes in Wisconsin typically have some problems with algae bloom each summer and the ones in western Wisconsin causing so much discomfort this year are being fueled by a perfect storm, Vennie said. The last month has seen little rain, warm, sunshiny days and little wind.

The blooms just sit there, growing, then decaying and smelling.

"Some people say they have gotten nauseous and vomited from smelling it," said Ken Schreiber, a Wisconsin Department of Natural Resources water quality specialist.

Officials have banned recreational activities at some lakes in Washington state because of blooms. And in Oregon, the blue-green algae is the number one water quality issue, Carmichael said.

Yet other countries have worse problems, Carmichael said, because many have waters with even more nutrients than exist in U.S. lakes.

In France, a horse died on a beach in July after falling into some decaying algae sludge. Last year, the Chinese government brought in the army to remove the slimy growths so the Olympic sailing competition could be held.

Stephanie Marquis, a spokesman for the Wisconsin Department of Health Services, said her agency had received 41 complaints related to health concerns with blue-green algae so far this season. Rashes, sore throats and eye irritation among the problems, she said.

In Minnesota, Matt Lindon is a pollution control specialist for the state and he called 2009 a typical year for complaints about algae scums. But for some reason this summer, Bagley Lake in northwest Minnesota, an "historically clean lake," generated respiratory and odor problems, he said. "It may be related to the water level or some new runoff source," he said.

Loren Hake, 71, has lived about two blocks from a Lake Menomin in western Wisconsin since 1963.

He feels like a prisoner in his own home, isolated by a stench "something like a pig pen" that forces he and his wife to run the air conditioner although it's not that hot because they can't leave the windows open, he said. For the first time, the couple hasn't set on an outside deck because of the smell from the algae-covered bay.

"I don't know what they can do about it," Hake said.

There's little anybody can do besides wait for cooler temperatures, Vennie said.

John Plaza, president of the Chetek Lakes Protection Association, which represents six lakes in northwest Wisconsin, said farm runoff, lawn fertilizers, septic systems and even ashes from leaves being burned on the shorelines are among factors contributing to the algae problems.

"I have been a user of these lakes since 1962," he said. "I have never experienced anything like this before. It's nasty. People are saying we can't live with this any more."