What's turning Southwest Florida's shores brown? It's not red tide

The sand was white, but the murky, brownish water at some beaches in Collier and southern Lee counties continued to keep some would-be swimmers at bay Monday.

Discolored water has been reported at multiple locations, including Barefoot Beach, Seagate Beach and the Naples Pier, according to Naples' Natural Resources Manager Stephanie Molloy. Beachgoers on social media also reported a similar discoloration at Bonita Beach on Sunday.

But while red tide spells have ravaged Southwest Florida beaches and sea life for months, the discoloration is being caused by a bloom of a nontoxic diatom, called Cylindrotheca, Molloy said.

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"There's lots of different species," she said. "When the conditions are right, they bloom."

But unlike red tide, which can cause respiratory issues and coughing for beachgoers, the diatom does not produce a toxin, Molloy said.

"It isn't a human health risk," she said.

Florida Gulf Coast University marine sciences professor Michael Parsons said the diatom can grow "a lot faster" than the red tide organism, Karenia brevis, and may be winning the battle for the nutrients in the water.

"It will almost always be outcompeted by diatom," said Parsons, director of FGCU's Coastal Watershed Institute and the Vester Marine and Environmental Science Research Field Station.

The diatoms tend to grow well in calmer water, he said. 

"This year it's been pretty quiet," Parsons said.

The water on Sanibel Island’s Bowman’s Beach also has been darkly discolored by a bloom of another microorganism, a dinoflagellate like the one that causes red tide called Peridinium, “but it’s not toxic,” said Sanibel-Captiva Conservation Foundation research scientist Rick Bartleson.

In Lee County red tide cell counts have been lower recently, but not enough to safely call it a trend, he said.

On Monday, beachgoers could still find dead grass eels, smaller crabs and fish scattered across the shores in Collier.

Previously:Murky waters at Naples Pier keep swimmers away

Although the diatom causing the discolored water is not toxic, it can contribute to an imbalance in the water's oxygen levels, which can lead to fish kills if the oxygen levels drop far enough, Parsons said.

The grass eels are "just more sensitive probably" to the lower oxygen levels and essentially suffocate, he said, which may be why they're washing ashore now.

In Collier, the brown water started showing up last week and has been moving back and forth between Barefoot Beach and the Naples Pier, said Rhonda Watkins, a senior operations analyst with Collier County Pollution Control.

"Most of the Naples beaches are also experiencing low oxygen levels and species that aren’t typically affected by red tide toxin (crabs and sand dollars) are dying from lack of oxygen," Watkins said in an email. "We still do have red tide at some beaches and offshore along the entire Collier coastline."

More:Scientists to test samples of thick green algae spotted in Bonita Springs

Watkins recommended that those who are sensitive to red tide or have chronic breathing illnesses should avoid the beach. 

"Other bottom-dwelling fish such as flounder, eels, batfish and toadfish are also dying and washing ashore which could be from a combination of red tide toxin and lack of oxygen," she wrote. 

The only Collier beach currently not experiencing discolored water or dead fish appears to be Marco Island, Watkins said, although she added that the blooms are "very patchy and conditions can change quickly."

Matt Wells, who works at Cabana Dan's at Vanderbilt Beach, said he first started noticing the "coffee-brown" discoloration about four days ago.

Few, if any, beachgoers went into the water Sunday, causing the little concession hut to close early "just because there was no customers on the beach," he said.

"Nobody was going in the water," Wells said.

Monday morning presented a similar picture at Vanderbilt Beach and the Naples Pier: beachgoers in chairs and on towels soaking up the sun with most steering clear of the water.

Wells said he has been observing a different species washing ashore nearly every week.

"Last week we had a lot of blue-shell crabs," he said. "This week we got a lot of eels, which are abnormal down here, and flounders."

Kevin Swede was one of the few who braved the brown seas Monday morning, wading ashore from a boat he had been on to see what the conditions looked like seaside.

He estimated that the brownish discoloration reached about 100 yards from the shore into the Gulf, where the water was clearer. 

"When we came in, obviously, it's the brownish, brackish," said Swede, 32. "Dead eels, shrimp, crabs. But if you go out a little bit farther out, it's kind of like, looks normal."

Naples Harbormaster Roger Jacobsen said he remembers similar conditions at local beaches about a decade ago. Back then, "everybody thought it was an oil spill," he said.

"Because it almost has that (look)," Jacobsen said. "Especially when you look at what's accumulating. ... And it's not. It's not an oil spill."

But a reprieve from the murky conditions may be in sight.

Parsons, the FGCU scientist, said forecast models predict easterly and southeasterly winds this week, which would help push the diatoms back into the more nutrient-poor Gulf. 

There, the diatoms would basically "starve" and dissipate, he said.

Fort Myers News-Press reporter Amy Bennett Williams contributed to this story.

How you can help

Officials are asking for the public's help in reporting beach conditions, good or bad, using a smartphone app called MOTE CSIC.

Mote Marine Laboratory & Aquarium in Sarasota, NOAA, FWC and the University of South Florida use the information to track and forecast harmful algal blooms.

Beachgoers can also check out local conditions before they go at www.visitbeaches.org.