They don't know if the toxins reach drinking water sources or if they survive treatment, said researchers at a Florida Department of Health gathering to share study results from a three-year, $3 million Centers for Disease Control grant.

The scientists do know that the toxins cause a wide range of ill effects for people, from rashes and respiratory problems to cancer.

Their research is aimed at understanding the health effects of harmful algal blooms, or HABs.

HABs are naturally occurring toxic algae or blue-green algae. Under the right conditions, they reproduce rapidly to form a bloom. The blooms can release toxins into the water or air, or both.

Scientists at the meeting say they are gradually learning about the health impacts of red tide. They remain concerned about effects that may come from toxic blue-green algae.

"Pretending it's not there is not an appropriate way to deal with it," said Lora Fleming, a researcher from the University of Miami's Miller School of Medicine.

She said studies might put people's fears to rest. "Maybe we'll be reassured."

Maybe not.

The compounds that blue-green algae -- more accurately known as cyanobacteria -- produce are known carcinogens with long-term exposure as well as being tumor promoters, researchers said.

But so far their attempts to find out if those toxins show up in treated drinking water have been stymied by utilities unwilling to take part in a study.

Florida is home to more kinds of toxic algae and cyanobacteria than anywhere else in the United States and perhaps the world.

Better known as pond scum, cyanobacteria can look like green hair or like someone dumped bright green paint on the water.

Blooms of several species are showing up more and more in Florida's springs, lakes and rivers, and along its coasts, mostly where rivers bring runoff to the Atlantic and the Gulf of Mexico.

The Panhandle's Lake Munson has supported a bloom for two years that has locals concerned, said Chris Williams, an aquatic toxicologist for GreenWater Laboratories in Palatka.

"They are starting to worry about health effects," he said.

Springs in North Florida are seeing the blooms as well, and visitors are reporting rashes, itching and respiratory problems.

And in 2005, the St. Johns River lay under a blanket of blue-green algae, as the St. Lucie Canal and the Indian River Lagoon have repeatedly done in recent years.

On the state's west coast, a saltwater type of cyanobacteria called Lyngbya with compounds known to speed tumor growth in animals appeared in May around Sanibel and persisted through the summer.

"This summer has just been terrible," said Steve Brown, former Sanibel mayor and current City Council member. So much so that officials are considering legal action against the Army Corps of Engineers, the South Florida Water Management District and other parties they blame for the nutrient-rich Caloosahatchee River releases that they say fuel the bloom.

The Environmental Protection Agency has yet to set cyanobacteria standards for drinking water.

"We know so much about red tide and so little about blue-green algae in our drinking water supply," said Andrew Reich, coordinator of the Aquatic Toxins program for the Florida Department of Health. "We've got to go there."

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