Third species of algae, fueled by decomposing fish, is found blooming in Southwest Florida waters

There's a third type of algae lurking in local waters. 

The good news is that it's not toxic. The bad news is that it can impact marine life and put off an unpleasant odor. 

Oscillatoria algae

"We’ve been seeing this really bright green species called Oscillatoria, and it seems to be prevalent based on the availability of new nutrients from decomposing fish," said Rick Bartleson, a water quality scientist for the Sanibel-Captiva Conservation Foundation.

You read that right: one type of algae, red tide, has caused massive fish kills in Southwest Florida since October, and now the dead fish are fueling a completely different species of algae. 

"If it’s floating upside down it’s brown and if you flop it over its green," Bartleson said. "We don’t know of any toxin (associated with this species)." 

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The algae can look like paint sprayed on a beach, or even appear as large brown chunks of floating organic material. 

It seems to be blooming in between the other two algae blooms, which have plagued this area since June. 

The red tide bloom has dumped millions of pounds of fish on Lee County beaches and shorelines this month, and hundreds of sea turtles have died in Southwest Florida over the past three months. 

More:Environmental experts say Southwest Florida's algae blooms may not ease until winter

A blue-green algae bloom started on Lake Okeechobee in early June and quickly spread to the Caloosahatchee and St. Lucie rivers. 

Both the red tide and the blue-green algae in the river are toxic. 

Seen in Collier too

Collier County reported seeing similar conditions with Oscillatoria, the non-toxic species.

"If you live on a saltwater bay, you may have seen this algae floating on the surface," a Collier County Facebook page reads. "These mats are mixed forms of marine algae that grow on the bottom of the bay. As they die, they peel off the bottom and float to the top. These mats are not harmful, but may produce some odor as they decay."

Red tide counts along the coast have ranged from background levels to 1 million cells per liter and higher. 

Fish kills and breathing irritation in humans can start when levels reach 10,000 cells per liter, according to the Florida Fish and Wildlife Conservation Commission. 

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Bartleson said this new type of algae can be harmful though not toxic to the ecosystem because it keeps light from reaching seagrasses and causes oxygen levels to shrink. 

"Whenever you have something growing over the sea grasses it’s shading the seagrasses and blocking water and carbon dioxide exchange in the grasses," Bartleson said. "When it accumulates along the shoreline it impacts everything because the oxygen gets sucked out of the water."

Beach hazard advisory

The National Weather Service extended a red tide beach hazard advisory for Lee, Charlotte and Sarasota counties through Monday. 

Current levels will cause intense symptoms from the Tampa Bay area south to northern Collier County, according to the National Oceanic and Atmospheric Administration. 

The University of South Florida's College of Marine Science predicts that the red tide will move generally north over the next three days. 

Connect with this reporter: Chad Gillis on Twitter.