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Red tide is a harmful algal blooms that can sicken or even kill local wildlife. It also causes respiratory issues in humans and other animals. Wochit

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A red tide bloom that's been lingering along the Southwest Florida coast for the past two months has spread out and grown more dense in recent days. 

The Florida Fish and Wildlife Conservation Commission is reporting counts of 1 million cells per liter of Karenia brevis (the organism that causes red tides in this region) and higher in Lee, Charlotte, Sarasota and Manatee counties. 

"I got 2 million cells per liter just south of Sanibel," said Rick Bartleson, a water quality scientists at the Sanibel-Captiva Conservation Foundation who takes samples and reports them to fish and wildlife. "I also found 2 million cells per liter about a-mile-and-a-half south of Sanibel, and all of the samples I took (in other areas along the coast) had Karenia."

More: Red tide found at very low levels at Naples beaches, dead fish offshore Gordon Pass

More: Red tide disperses off Lee County while Collier waters are clear

More: Patchy algae bloom moves north along Collier County shore, but it's not red tide

Fish kills can happen when counts reach 10,000 cells per liter and have been reported in Lee, Charlotte and Sarasota, although Bartleson said the strongest part of the blooms is offshore. 

Karenia brevis is a natural part of the ecosystem but can bloom to high concentrations when conditions favor it. 

Blooms typically start off around Sarasota and work their way south toward Collier County and Marco Island. 

This bloom probably started in October as several cormorants with red tide poisoning were taken to the Center for the Rehabilitation of Wildlife, or CROW, on Sanibel then. 

These birds are the canary in the coal mine for red tides because they're far-ranging birds that feed along the coast and just offshore. 

Cormorants eat small fish that have accumulated the red tide in their system, and the birds then get sick themselves. 

Red tide also kills fish, marine mammals such as dolphins and manatees, and sea turtles. 

Bartleson said the dense areas of red tide are large and spread along the coast. 

"This one patch we saw on satellite imagery was 2 miles wide, so they’re not really small patches at all," he said. "A patch a fisherman mapped for us was 3 miles wide."

The dense patches are likely killing fish, but the dead fish are, for the most part, out in the Gulf of Mexico and not on local beaches. 

That could change if winds come out of the northwest, as they often do during cold fronts. But, those winds can also cause weaker patches of red tide to disburse. 

A cold front has started to work its way through the area, and north winds are expected to blow for a few days. 

But Bartleson said he doesn't expect weather will have much impact on this large bloom. 

"The area offshore is huge judging from the satellite images, so it sort of doesn’t matter which way it’s going," he said. 

Environmental groups are paying attention to the bloom as well. 

John Cassani, with Calusa Waterkeeper, said he's worried that the bloom is being fed by excess nutrients running off the Southwest Florida landscape and from Lake Okeechobee. 

"It looks like it’s just staying here, in northern and central Lee county and southern Charlotte, and it’s not going away," Cassani said. "It just seems to be persisting here and I think it does renew that discussion about (stormwater and Lake O releases feeding the blooms). I think the intensity, in terms of densities and duration, may be contributing to its persistence here."

Flows from Lake Okeechobee and local stormwater runoff have been very high this year as several storm events added up to create the wettest wet season on record. 

Bartleson said he hopes the red tide pattern doesn't follow similarly wet years. 

"We started seeing (more of) it in the middle of November, so it’s been going on for a month and a half, but we’re hoping it will go away soon," Bartleson said. "But after high flows in 2005 the red tide stuck around for the whole year, until 2006. We hope it doesn’t do that again."

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