A sign is posted for depositing dead marine life from the

A sign is posted for depositing dead marine life from the "red tide" bacteria into dumpsters is seen at Bay Vista Park on July 21, 2021 in St Petersburg, Florida. / Getty Images

The harmful "red tide," which has been known to discolor coastal waters and kill marine life off the coast of Florida, has returned for another year.

The toxic organism that paints the waters red was detected in February and was found at higher-than-normal levels in several Southwest Florida counties in recent days, state officials said.

Since it returned, grisly photos of dead fish washing up on Florida beaches have proliferated, and federal authorities are warning people of the possibility of respiratory irritation from contaminated air.

Why it's called "red tide"

Oceans and other bodies of water are filled with algae, a small number of which are toxic but often exist in such small concentrations that they pose little danger to people and marine life around them.

When those toxic aquatic organisms multiply, they can form what are known as harmful algal blooms, which have been reported in every coastal U.S. state.

Though there are dozens of potentially dangerous algae species, one known to make an appearance each year along Florida's Gulf Coast is called Karenia brevis, a microscopic organism with "whip-like appendages" called flagella it uses to swim.

When Karenia brevis algae multiply in large numbers, they can form blooms that turn the water a reddish-brown hue, giving the phenomenon the moniker "red tide."

Red tides have been documented along Florida's Gulf Coast as far back as the 1840s, state officials said.

Scientists can't predict when red tides will occur, but experts in Florida are researching prevention and mitigation measures to minimize their impact.

The toxic algae can kill fish and make humans sick

Karenia brevis produce what are known as brevetoxins, which can kill marine life and birds.

The red tide organism can also cause health problems in humans, such as skin irritation. Brevetoxins that have become airborne may cause those near the beach to develop a cough or congestion.

People who eat shellfish affected by brevetoxins can also come down with Neurotoxic Shellfish Poisoning, which can lead to gastrointestinal problems, tingling feelings in the mouth, the reversal of hot and cold sensations and other symptoms.

Florida's Fish And Wildlife Conservation Commission warns people to not swim in or around red tide waters over the possibility of skin irritation, rashes and burning and sore eyes. People with asthma or lung disease should avoid beaches affected by the toxic algae.

If you come into contact with red tide water, Florida health officials recommend washing off with soap and water and going to an air-conditioned space.

What's happening in Florida

The Florida Fish and Wildlife Conservation Commission said Friday that it had received reports over the previous week of respiratory illness in humans and dead fish in Pinellas, Manatee, Sarasota, Charlotte, Lee and Collier counties. The incidents were suspected to be caused by red tide.

Local TV stations showed footage of dead fish washing up on beaches, and other marine life has also been reportedly affected by the toxic algae.

The threat to humans was still present, too. The National Centers for Coastal Ocean Science on Monday was forecasting a high risk of respiratory irritation from red tide at certain beaches in Charlotte, Manatee, Pinellas and Sarasota counties.

According to the TV station Bay News 9, local businesses were concerned that the red tide would drive away tourists and negatively impact south Florida's economy.

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