What You Should Know About Florida’s Red and Green Slime Crisis

A short guide to the toxic red and green pollution in Florida’s waterways that’s killing marine animals and threatening residents’ way of life.

Alex Kuizon covers his face as he stands near dead fish at a boat ramp in Bradenton Beach, Fla., on  Aug. 6, 2018. Normally crystal clear water was murky, and the smell of dead fish permeated the air.
Alex Kuizon covers his face as he stands near dead fish at a boat ramp in Bradenton Beach, Fla., on Aug. 6, 2018. Normally crystal clear water was murky, and the smell of dead fish permeated the air. (Chris O'Meara / AP)

Florida is in crisis as, once again, outbreaks of red and green slime take over the state’s iconic beaches and waterfronts.

Whether it’s the red tide on Florida’s southwest coast, or the green slime on rivers, lakes, and other freshwater habitats across the state, these persistent, harmful outbreaks aren’t natural. The outbreaks are fueled by toxic pollution from sewage, fertilizer, and manure. And they’re threatening people’s health and livelihoods, as well as killing off seagrass beds and massive amounts of marine life.

Here’s a breakdown of the toxic outbreaks, why they’re harmful, and the concrete steps we can take to prevent them in the future.

1. What’s causing the algae outbreaks?

It’s natural to have some algae in the water column, but decades of fertilizer, manure and sewage runoff have boosted phosphorus and nitrogen levels, making toxic algae grow out of control and poisoning Florida’s waters.

Lake Okeechobee — once a natural South Florida jewel— is one example. The lake has long received massive amounts of agricultural waste from dairies, cattle operations, industrial-sized sugar cane fields, large plant nurseries and croplands from north and south of the lake. Human waste from rapid development north of the lake, as well as population growth, has also added to this pollution.

For decades, Earthjustice and others have warned about the harm from industrial dumping in the lake. When the lake level gets too high and threatens the flood control dike surrounding Lake Okeechobee, water managers send polluted water east through the St. Lucie River to the Atlantic and west through the Caloosahatchee River to the Gulf, sparking algae outbreaks that kill marine life, shut beaches, and wreck neighborhoods and businesses.

As the blue-green cyanobacteria decays, the released phosphorus and nitrogen feed and worsen the red tide along the coast. These outbreaks are super-charged by climate change’s warmer waters, hotter temperatures, and intensifying storms.

2. What are the health risks of toxic algae?

The red tide organism, Karenia brevis or K. brevis, produces toxins that can kill fish and other vertebrate species that ingest them by affecting the central nervous system.

Environmental impacts include massive fish kills; marine mammal, sea turtle and sea bird mortalities; and impacts on benthic communities including sea grass and coral community die-offs.

Red tide is also dangerous for humans. Eating shellfish contaminated with the K. brevis toxin can cause neurotoxic shellfish poisoning, with symptoms like vomiting and nausea and a variety of neurological difficulties.

Regulators ban recreational shellfish gathering during red tide events and commercial shellfish operations strictly monitor for red tide. But people can also be exposed through the air, causing respiratory and eye irritation, particularly in those with severe or chronic respiratory conditions such as emphysema or asthma. The algae’s airborne spread has shown to be affecting people as far as 10 miles away.

Blue-green slime is also toxic to wildlife and humans. Touching or ingesting water containing this cyanobacteria can cause symptoms such as skin rashes, runny nose, sore throat, allergic reactions, severe gastroenteritis, liver or kidney toxicity, and neurological problems.

The International Agency for Research on Cancer, a specialized division of the World Health Organization, has determined that microcystin, one of four major toxins made by blue-green algae outbreaks, is possibly carcinogenic to humans.

Toxic algae outbreaks have also killed pet dogs in Florida and elsewhere.

Florida set a grisly record for manatee deaths in 2021, with more than 1,000 manatees found dead in Florida waters, mostly in the Indian River Lagoon on the southeast coast. The manatees starved because algae outbreaks killed off the seagrass beds they depend on for food. Only an estimated 5,700 manatees exist in Florida.

3. What’s the state doing about the algae outbreaks?

Florida Gov. Ron DeSantis’ administration and the state legislature have done little to stop the pollution that’s causing the crisis.

In fact, the state and its political leaders have done nothing to stop this pollution for decades, repeatedly refusing enact protective legislation to control the outbreaks or enforcing the few laws that are on the books.

The DeSantis administration and Florida legislators continue to kick the can down the road, and officials even gutted water quality monitoring as the algae crisis has worsened.

The political inaction is largely due to the stronghold that polluter industries like Big Ag and developers have over Florida’s politicians. Agricultural and development polluters give massively to political campaigns and committees. For years legislators and regulators have continuously sided with powerful polluters like the sugar, development, and cattle industries.

Meanwhile, the algae crisis continues to devastate the state’s marine ecologies, cost the tourism and fishing industries billions if not trillions of dollars in lost revenue, and put Floridians’ health and quality of life at risk.

4. How can we prevent these toxic outbreaks?

“Calling these outbreaks ‘natural’ is like calling a rat infestation ‘natural.’ Sure, rats exist in nature. But when you have an infestation, there’s probably something else going on.”

– Alisa Coe, Senior Attorney
Lead counsel for conservation groups in the two decades-old Everglades water pollution litigation

First, we need to hold our politicians accountable for supporting the falsehood that these toxic outbreaks are “natural.”

“Calling these outbreaks ‘natural’ is like calling a rat infestation ‘natural,’” says Earthjustice attorney Alisa Coe.

“Sure, rats exist in nature. But when you have an infestation, there’s probably something else going on.”

Second, we know how the nitrogen and phosphorus in sewage, manure, and fertilizer tip Florida’s delicate ecological balance.

And we know that climate change is adding pressure to these problems, which makes the need for action all the greater. We have a responsibility to demand action.

5. What is Earthjustice doing?

Earthjustice has spent years battling pollution of Florida’s waterways while state and federal officials have fought us at every turn. Government’s failures to address pollution are the main reason we are where we are. We will continue fighting the assault on the truth of what is happening, and to get meaningful regulations to restrict this type of pollution.

We are also in court defending the will of Floridians to spend a percentage of tax dollars on conservation land buying, which 75 percent of Florida voters directed in a 2014 statewide vote.

The Water and Land Conservation Constitutional amendment was supposed to generate about $750 million dollars annually for 20 years to buy conservation land, but the state has instead used the money for salaries and agency operating expenses.

We are now arguing on appeal in the Florida Supreme Court in a lawsuit we first filed in 2015. Conservation land acts as an important filter to polluted water and is needed now more than ever to protect our waterways.


Earthjustice’s Florida Office was established in 1990. Water rules over much of the state. But water quality has been declining for decades. From locations in Tallahassee and Miami, Earthjustice attorneys in the Florida regional office work to protect the state’s precious waterways from agricultural and sewage runoff. We will restore Florida waters to the astounding natural resource they once were.