CLEVELAND, Ohio -- Toxic algae -- already a summer plague of Lake Erie and hundreds of shallow inland lakes -- might be even more dangerous than first believed.

A team of biologists and endocrinologists reported this week that unknown organic chemical harbored in the algae -- separate from the known toxin microcystis -- may be interfering with certain fish reproductive systems.

It isn't clear whether the chemical, which has yet to be isolated or named, might be affecting other fish species, animals or even humans living on the shores and drinking the waters of Lake Erie or other lakes where the algae is emerging.

"The main point is that there is a lot more going on here than just the toxin in this algae," said Ted Henry, a Tennessee research professor now at the University of Plymouth, England who oversaw the study's author, doctoral student Emily Rogers.

"There needs to be more work done to establish under what conditions the algae produces these substances and how dangerous they are, that's for certain."

The paper, published in the journal Environmental Science & Technology, was the result of a four-year study supported by the National Oceanic and Atmospheric Administration. It was aimed primarily at deciphering the source and discovering a solution for annual algal outbreaks in western Lake Erie, Henry said.

The study also suggests that algae, although a naturally occurring substance, may be a catalyst for sex changes and other reproduction problems in fish. Scientists long believed those changes were only caused by human-made pollutants in the water.

"We believe this is also the first study to suggest that estrogenic response in fish species -- feminizing fish and other changes in reproduction -- might be coming from a natural source such as algae," he said in a telephone interview from Plymouth.

In any case, reports that algae might have another weapon in its arsenal could be devastating news for lake lovers, environmentalists, scientists and government policy makers in the Great Lakes.

Algae already the bad guy

"We're already seeing more and more algae and higher concentrations each summer," said Doug Keller, water-services superintendent for Sandusky's water treatment plant. "Now, if you're telling me that blue-green algae might also be affecting fish in this way, that's worse news."

Keller had formed an association of 22 water plant managers along Lake Erie's southern shore in 2006 in an attempt to better notify each other when algal blooms appeared. Cities like Toledo and Sandusky can spend thousands of dollars more a day to treat drinking water to kill the toxic algae, he said. NOAA has also tested a warning system.

Blue-green algal blooms overwhelmed Grand Lake St. Marys in west central Ohio in 2010, where several family pets died from exposure to the toxic water. Outbreaks have also shut down dozens of other beaches in recent years in Minnesota, Michigan, Illinois and Indiana.

Satellite images of western Lake Erie have shown algae on the increase. They had been absent for nearly 20 years in the wake of the more stringent water quality laws of the early 1970s.

Scientists have most often blamed high concentrations of phosphorus, most likely from animal feeding operations and farms in western Ohio as well as high water temperatures for the increase. The summer of 2010 was considered to be the worst in 30 or 40 years.

Both NASA and NOAA, as well as by a private company, have been scrambling to come up with a better way of identifying blue-green algal blooms by using hyper-spectral photography from airplanes, satellites or tethered blimps hovering over Lake Erie.

More studies coming

A second report has yet to be released on the how the chemical affected channel catfish taken from western Lake Erie, Henry said in a telephone interview Thursday. The current report only explores how the chemical affected zebra fish, a fish not found in Lake Erie, but used by scientists because they can easily track changes in its DNA.

"We want to use this information to apply to fish that are environmentally relevant to the Great Lakes, specifically the western basin of Lake Erie," Henry said. "That's our real target because that's where everything's happening, even though blue-green algae is a growing concern internationally."

Officials from the Ohio EPA, Department of Health and Department of Natural Resources were hesitant to comment on the new study before reading it thoroughly.

Henry's team, however, called "for a revision of environmental monitoring programs to watch for these new substances" in a news release.

"That may sound a little strong, putting a new policy in place based on one study," he said. "But there's no harm in testing now for something as problematic as endocrine disrupters in the water."

Henry said the zebra fish was used as a research subject because its entire genome has been sequenced, making it easier to tell if a chemical has had an effect on the expression of specific genes.

"The result was a serendipity situation, really," he said. "We did not anticipate an effect consistent with an estrogenic substance."

He said it was not likely that the algae was merely "carrying" the chemical from an outside source in the water because the researchers had used a controlled water source, not water from Lake Erie, for example.

Henry said the report is likely to cause " a lot of people to reconsider a lot of previous data about endocrine disruption."

VIDEO: University of Toledo researcher studies toxic algae on Lake Erie in 2008