Florida Coasts Are Currently Being Overwhelmed By Dead, Rotting, Stinky Fish


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

dead fish

Tampa Bay after a previous "red tide". Image credit: Mark Winfrey/

Tampa Bay in Florida, with its abundant mudflats, mangrove swamps, and tidal channels, has long been home to some amazing biodiversity. While climate change and human settlement have taken their toll, back in the 18th century, its waters were so full of fish that they overwhelmed boats.

This summer, the Bay is once again overwhelmed with fish – but with a truly gruesome twist. Over 600 tons of dead, rotting marine life has been washed up onto local beaches since late June – and officials aren’t quite sure why.


"The bay is really hurting right now," Tampa Bay Estuary Program Assistant Director Maya Burke told NPR. "It's significant numbers of dead fish all up and down the food chain, from small forage fish all the way up to tarpon, manatees, dolphins. ... If it's swimming in the bay, right now it's washing up dead."


By June 2021, Florida had already lost more manatees than in any other year on record, with algae blooms the likely culprit. The same is true for the masses of fish that are now turning up dead along the coast.

Florida “red tides” turn up along the state’s Gulf Coast about once a year, when the microscopic alga Karenia brevis “blooms” – releasing a potent neurotoxin. This has always been in Florida, but warming waters fuelled by the climate crisis have meant that K. brevis populations have flourished in recent decades. For Tampa Bay’s human inhabitants, that means coughs, sneezes, and in extreme cases, a trip to the emergency room. But for local wildlife, it’s deadly.

Nevertheless, this year is particularly bad – and not just because of the stench. The timing is all wrong, local experts say: red tide doesn’t usually come in from offshore until later in the year, University of South Florida physical oceanography professor Robert Weisberg told the Tampa Bay Times. Even worse: results from his lab, which forecasts the movement of red tide, suggest the phenomenon isn’t going anywhere for a while.


“The prognosis is not all that good,” he said.


Although we know the red tide is to blame for the mass deaths, what is less clear is what’s to blame for the red tide itself. Water samples from local Pinellas county have registered concentrations of red tide up to 17 times greater than the level considered “high”, but scientists have yet to find a “smoking gun” for the unusual blooms, said Burke.

And in fact, the cause may be multifaceted, according to local experts. Unusual weather patterns may be to blame for pushing the red tide further into shore than normal, Weisberg explained. Once there, the algae found a feast waiting for them in the form of a wastewater spill from a fertilizer plant, and populations exploded.

“If you give it the right suite of nutrients, the concentrations can escalate very rapidly,” Weisberg told the Times.


“That’s textbook what we’re seeing right now,” agreed Burke. “We have no reason not to link those two things together.”


For now, efforts are aimed at clearing the masses of fish corpses from the beaches – and local residents aren’t exempt. The city of St Petersburg, where most of the carcasses have washed up, has provided dumpsters in several parks for locals to dispose of any dead fish they find. The clean-up isn’t just a priority because of the smell though – as the fish rot in the water, the bodies release nutrients that feed the algae, causing a deadly self-sustaining cycle.

“It’s here. It’s bad. And there’s not much we can do other than make sure we’re all communicating well,” Florida Fish and Wildlife Conservation Commission Director Eric Sutton told the Times. “There’s no signs that necessarily it’s going to be coming to an end soon, but I’ve learned enough not to try to predict Red Tide either.”

 This Week in IFLScience

Receive our biggest science stories to your inbox weekly!


  • tag
  • fish,

  • algae,

  • algal bloom