CLEVELAND – Giant floating fields of algae are back in strength this year on Lake Erie and scientists are trying to figure out why.

The blooms of the pea-soup colored algae – so big they've been showing on satellite photos – are toxic to fish and small animals and irritating to humans. The lake once notorious for its pollution is cleaner than ever, yet the algae continues to thrive.

“Algae is a big deal, especially the microcystis, what is often called the blue-green algae,” said Tom Bridgeman, a professor of environmental science at the University of Toledo's Lake Erie Center. “It's not aesthetically pleasing when it gets on boats or rots on the shore, but it can also be a health hazard.”

Nine of 11 samples taken Sept. 3 from near West Sister Island, northeast of Toledo, were more toxic than guidelines set by the World Health Organization, said Geoffrey Horst, a Michigan State University graduate student who studies the algae. It won't kill people, but at minimum it's going to give swimmers a rash.

Water utilities along Ohio's Lake Erie shore spend thousands of dollars a day to kill the thick algae and to treat the bad smells and bad tastes that the organism causes, officials said.

But it's not going away.

“It's now blooming in the proportions that it was in the bad old days of the 1960s and early '70s,” Bridgeman said. “There's a mystery to it because the lake seemed to be getting cleaner, but now the algal blooms are worse.”

Even dead, the algae poses a problem: Decomposition of dead algae uses up oxygen and creates oxygen-free dead zones in the lake.

“There has already been a fish die-off in Lake Erie this season,” said John Hageman, laboratory manager at Ohio State University's Stone Lab on Gibraltar Island.

Researchers suggest the algae might be blooming because it's fed by abundant phosphorus, which is running into the lake from increased suburban development.

“The same nutrient-rich fertilizers which cause our grass and crops to grow can cause the algae to grow in the lake,” said Bridgeman, who calls the algae “Green Kool-Aid.”

Information from: The Plain Dealer, www.cleveland.com