Weird Water: Aerial photos show puzzling brown streaks around Sanibel Causeway

Amy Bennett Williams
Fort Myers News-Press
Calusa Waterkeeper volunteer pilot Ralph Arwood photographed brown-streaked water near Bunche Beach and the Sanibel Causeway March 15.

Scientists are working to understand what’s staining water brownish to olive drab near Bunche Beach and the Sanibel Causeway in south Lee County where the Caloosahatchee River meets the Gulf of Mexico.

Photos shot by volunteer Calusa Waterkeeper pilot Ralph Arwood of the region Wednesday showed wide opaque-looking streaks.

The question now: What’s causing them?

Answers could range from muddy water stirred up by a recent windy front to the start of a harmful algae bloom, scientists say. So far, they haven't found the red tide microbe in nearby water specimens. 

This photo from Calusa Waterkeeper pilot Ralph Arwood shows different colored water near the Sanibel Causaway that has Waterkeeper John Cassani wondering if a bloom is developing. The key question: What it it?

The rough weather also is causing mats of harmless red drift algae mixed with broken-off blades of seagrass to wash ashore along the causeway islands and Bunche Beach, which didn't appear to deter St. Patrick's Day sunbathers.  

Calusa Waterkeeper John Cassani says he’s open to the idea that the weird-looking water could be turbidity caused by suspended particles, but he’s concerned about the streaks’ clearly defined borders in the photos, which are more characteristic of algae blooms.

“The edge of turbid water is not usually that defined and typically more diffuse. Last year about this time we saw similar blooms nearshore. My best guess until I can get a sample is a diatom bloom.”

Mud and drift algae create a design on a beach near the Causeway  in south Lee County  on Thursday, March 17, 2022. Scientists are working to understand whatÕs staining water olive drab near Bunche Beach and the Sanibel Causeway in south Lee County where the Caloosahatchee River meets the Gulf of Mexico

Diatoms are a broad category of single-celled creatures, also referred to as phytoplankton, that are a key part of the food web. Some species can produce toxins harmful to humans and wildlife.

Cassani points to the poor water quality upriver in the Caloosahatchee, near I-75, possibly caused by consistent flows from Lake Okeechobee through the W.P. Franklin Lock in Olga, which make their way to the estuary.

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Bunche Beach on March 17.

Those flows result from a human-engineered system that's wreaked chronic havoc on the natural system. To reduce flood risk and drain land for development, humans dredged a river/lake connection and altered the water cycle more than a century ago. Restoration efforts are underway, but meanwhile, problems remain.

To maintain its salinity in balance for the plants and animals that live there, "The estuary needs the freshwater inflow, but the water is heavily polluted with nutrients," Cassani said, "and I fear we are beginning to see the cumulative effects nearshore with various blooms."

Beachgoers visit the Sanibel Causeway on Thursday, Feb. 3, 2022.

The good news is that those blooms don't appear to be red tide – so far.

Even so, in the first two weeks of March, Sanibel's Clinic for the Rehabilitation of Wildlife admitted 12 birds. The patients include gulls, cormorants, a black skimmer and a great blue heron, with red tide symptoms that could be a result of either red tide or another environmental toxin, said spokeswoman Haillie Mesics. 

A reddish egret forages for food at Bunche Beach in Fort Myers on Thursday, March 17, 2022. Scientists are working to understand whatÕs staining water olive drab near Bunche Beach and the Sanibel Causeway in south Lee County where the Caloosahatchee River meets the Gulf of Mexico

"All birds admitted with symptoms consistent with red tide poisoning were treated with an intravenous lipid emulsion therapy treatment," Mesics wrote in an email, "(which) consists of lipids and fats which bind to the toxins helping them to be excreted from the bird’s system and has very successful results if the bird survives the first 24 hours in care," she wrote. "The affected birds in care will continue to be closely monitored under supportive care."

In her most recent report on Lee County waters sampled Tuesday, Florida Fish and Wildlife Conservation Commission biologist Mary Harper, who works in the Fish and Wildlife Research Institute''s harmful algae bloom program, found neither Karenia brevis, which can cause red tide, nor Pyrodinium bahamense, which can produce saxitoxin, a potent neurotoxin.

The nonprofit Sanibel-Captiva Conservation Foundation also is sampling area waters. So far, specimens have shown several species of microorganisms, said foundation marine biologist Rick Bartleson, but none appear alarming.

Waves lap ashore at Bunche Beach  in Lee County  on Thursday, March 17, 2022. Scientists are working to understand what’s staining water olive drab near Bunche Beach and the Sanibel Causeway in south Lee County where the Caloosahatchee River meets the Gulf of Mexico

Turbidity takes a while to go down, Bartleson says, even after the wind slows, and the whipped-up particles can fertilize algal blooms.

"The resuspension can resupply diatoms with silica and phosphorus," Bartleson wrote in an email, "and they can double their biomass every day if they are happy. "

One of the dinoflagellates he found in a recent sample, Gonyaulax, could turn out to produce an interesting sight if it blooms in great numbers: bioluminescence – glowing water.  "One year a reporter asked why the water was bioluminescent and Gonyaulax was the main plankton in my sample along with Noctiluca, which is well known for bioluminescence," he wrote.