Originally published in the Fort Myers News-Press by Chad Gillis on August 15, 2024
There’s a fish kill going on in Matlacha Pass, and some water experts think it’s due to a lack of oxygen in the water.
Warm waters, the idea goes, have lowered oxygen levels in the water, and many species of fish are suffocating there.
“I think it’s related to the warming and relatively hot water,” said Calusa Waterkeeper Emeritus John Cassani. “When the temperature increases to this degree, it’s increasing microbial action. They need oxygen and they’re competing for oxygen with fish and shellfish.”
Cassani said warm waters are an underlying reason why we see fish kills on occasion during the summer in Southwest Florida.
Southwest Florida waters are warm this year at just over 90 degrees. That’s a few degrees higher than average, so while it’s not setting records, the high-water temperatures are still impacting the marine ecology.
Aerial photos taken by local pilot and Calusa Waterkeeper volunteer Ralph Arwood show tan-stained waters in the pass and hundreds of dead fishing floating in the water there.
Expert: TS Debby at least partially to blame
Jim Beever is a retired biologists and climate change planner and he said the event at Matlacha probably started with Tropical Storm Debby.
“With Debby, all that water runs past the water control structures and into Matlacha Pass, and that area is going to have a lot of nutrients and pollution,” Beever said. “So that probably contributed to the event. It’s an anoxic event of warm water combined with algae.”
Beever said the algae that blooms as a result of the nutrient and pollution loads from Tropical Storm Debby sucks up oxygen at night, making the problem worse.
“Warmer water can’t hold as much dissolved oxygen, and at places like Matlacha, with algae growing on the surface, those plants will use up oxygen too,” Beever said. “At night the plants will be using up the oxygen that’s in the water rather than adding oxygen to the water. And fish in that area that can’t get out of that area because they’re not mobile enough will end up suffocating.”
Beever said it’s possible the dissolved oxygen would not be a problem in Matlacha Pass if not for the stormwater running off Cape Coral.
Pollution leading to fish kills
“It’s very possible with warming we wouldn’t have fish kills so often if we also didn’t have pollution,” Beever said. “The lack of oxygen is causing the deaths but the reason why the oxygen is so low is a number of factors combined.”
Florida Gulf Coast University professor James Douglass wrote on Facebook that residents should get involved so they can learn about and fight for Florida’s ailing waters.
“Southwest Florida has chronic water quality problems that stem from decades of sprawling growth, weakened regulations and underinvestment in green infrastructure,” Douglass wrote on Facebook in a post that showed Arwood’s photos.
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