How can I find out what current red tide conditions are?

What is Florida red tide?

A red tide, or harmful algal bloom, is a higher-than-normal concentration of a microscopic alga (plant-like organism). In marine (saltwater) environments along Florida’s west coast and elsewhere in the Gulf of Mexico, the species that causes red tides is Karenia brevis, often abbreviated as K. brevis. To distinguish K. brevis blooms from red tides caused by other species of algae, researchers in Florida call it “Florida red tide.”

What causes a Florida red tide?

The Florida red tide alga, Karenia brevis, needs the following components to form a bloom. The first is biology — the organism must be present in the water and it must out-compete other phytoplankton. The second is the correct chemistry — this includes the appropriate temperature, salinity, and nutrients that it needs to grow and multiply. The third component is the right physical conditions to concentrate and transport K. brevis. The fourth component is ecology – the presence or absence of other life forms, such as other marine algae that may encourage or inhibit K. brevis blooms.

Has coastal (nutrient) pollution caused the Florida red tide?

In contrast to the many red tide species that are fueled by nutrient pollution associated with urban or agricultural runoff, there is no demonstrated direct link between nutrient pollution and Karenia brevis red tide formation or frequency (how often they occur). Florida red tides develop 10-40 miles offshore, away from human-contributed nutrient sources. Red tides occurred in Florida long before human settlement, and severe red tides were observed in the mid-1900s before the state’s coastlines were heavily developed.

However, once red tides are transported to shore, they are capable of using human-contributed nutrients for their growth.

Can coastal nutrient pollution worsen an existing Florida red tide that has moved to shore?

Yes, the scientific data available so far suggest that it is possible for nutrients flowing from land to sea — including natural AND human-contributed nutrients carried by storm water runoff and the input of rivers — to serve as additional “food” for growth of Karenia brevis red tide blooms that have moved to shore.

However, the process is very complex. K. brevis can use at least 12 sources of nitrogen and phosphorous nutrients, and some of those sources include human-contributed nutrients. Mote scientists partnered in major research efforts to gather that knowledge. Read a 2014 summary:

In short, we know human-contributed nutrients can affect a coastal red tide, and we must expand our data and monitoring efforts to confirm whether and how they did in each specific case.

Do freshwater outflows from Lake Okeechobee affect Florida red tide blooms that have moved to the Charlotte Harbor area?

To investigate this question, we must consider several variables with each bloom. Here are some key variables:

  • Nutrients, both natural and human-contributed, can be carried in these freshwater outflows, and have the potential to serve as additional “food” sources for K. brevis (see the previous question).
  • Salinity also matters. Riverine flows into the estuary have low salinity (less salt than the ocean), which is not conducive to K. brevis red tide growth.
  • Other algae species besides K. brevis live in the lake, river or Charlotte Harbor estuary, where rivers meet the sea. When nutrient rich-water flows down the river and into the estuary, the nutrients are available to freshwater species including blue-green algae (cyanobacteria) and estuary-dwelling algae species that can each form blooms. The potential linkages between nuisance algal blooms in the estuary, any freshwater algae carried in riverine flows to Charlotte Harbor, and saltwater K. brevis red tide (all collectively referred to as harmful algal blooms – HABs) is an important topic that needs further research.

Do blue-green algae (a group of species called cyanobacteria) affect Florida red tide (Karenia brevis)?

First, please note that some species of blue-green algae live in the ocean and other species live in freshwater, and each species has its own specific properties.

As of summer 2018, we aren’t aware of any data showing a direct relationship between the freshwater blue-green algae species in systems along Florida’s Gulf Coast and the ocean-dwelling Florida red tide caused by Karenia brevis. Freshwater blue-green algae are not suited to thrive in K. brevis’ ocean environment. However, as scientists we can’t rule out the possibility for one to influence the other indirectly (for instance, what are the fates of nutrients and any toxins in blue-green algae that reach saltwater and die?) – and the subject is worth continued investigation.

On the other hand, ocean-dwelling, blue-green algae species in the groups Trichodesmium and Synechococcus have been studied for their potential roles in Karenia brevis (Florida red tide) ecology. Trichodesmium forms extensive blooms offshore and “fixes” nitrogen into a more useable form. It is hypothesized that, as these bloom die and decay, they can provide nutrients to a developing K. brevis bloom. Ocean-dwelling species of Synechococcus can be a food source for some microscopic algae, and lab studies by others have suggested they have the potential to nourish K. brevis. Future research should investigate whether and how much this happens in the ocean.

Are Florida red tides always red?

At high enough concentrations, Florida red tide can discolor water a red, brown, rusty orange or even slightly greenish hue. Red tides caused by other algal species can appear red, brown, green or even purple. The water can also remain its normal color during a bloom.

Why are red tides harmful?

Many red tides produce toxic chemicals that can affect both marine organisms and humans. The Florida red tide organism, K. brevis, produces brevetoxins that can affect the central nervous system of fish and other vertebrates, causing these animals to die. Wave action can break open K. brevis cells and release these toxins into the air, leading to respiratory irritation. For people with severe or chronic respiratory conditions, such as emphysema or asthma, red tide can cause serious illness. The red tide toxins can also accumulate in molluscan filter-feeders such as oysters and clams, which can lead to neurotoxic shellfish poisoning in people who consume contaminated shellfish.

How does the Florida red tide caused by Karenia brevis, kill fish?

Karenia brevis, the Florida red tide organism, kills fish by producing a potent toxin (called brevetoxin) that affects the central nervous system of the fish. The toxin can also affect birds, sea turtles, mammals and other marine animals.

Are red tides new to Florida?

No. Red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida’s Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers in the 1500s.

Related article: Timeline of Florida red tides off the west coast

Do red tides occur anywhere else?

Yes, many algae species cause red tides all over the world. Yet, the organism that causes Florida’s red tide, K. brevis, is found almost exclusively in the Gulf of Mexico from Mexico to Florida. Florida red tides can be transported around the Gulf of Mexico as coastal waters move with winds and currents. Some red tides have even been carried by the Gulf Stream current into the Atlantic Ocean as far north as Delaware.

How long does a Florida red tide bloom last?

Red tides can last as little as a few weeks or longer than a year. They can even subside and then reoccur. The duration of a bloom in nearshore Florida waters depends on physical, chemical,  biological and ecological conditions that influence its growth and persistence, including sunlight, nutrients and salinity, as well as the speed and direction of wind and water currents.

Is the Florida red tide found in estuaries, bays or freshwater systems?

The Florida red tide can be found in bays and estuaries but not in freshwater systems such as lakes and rivers. Because K. brevis cannot tolerate low-salinity waters for very long, blooms usually remain in salty coastal waters and do not penetrate upper reaches of estuaries. However, other harmful algae, including cyanobacteria (blue-green algae), typically bloom in freshwater lakes and rivers.

Can we predict when and where a Florida red tide will occur?

Although the occurrence of a Florida red tide cannot be predicted, scientists can forecast its movement using wind and water current data once a bloom is located. Scientists also monitor the concentration of the red tide organism by collecting water samples routinely and in response to blooms. Red tide movement and concentration are important because the effects of a red tide, such as dead fish and human respiratory irritation, depend on these factors. The information provided by forecasting and monitoring allows people to make informed decisions regarding their beach-going activities. Currently, Mote Marine Laboratory, the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute and the National Oceanic and Atmospheric Administration provide status reports about Florida red tides to the public. (See full list of red tide resources at the top of this page.)

Online at:

FWC weekly status updates:
National Oceanic and Atmospheric Administration (NOAA):

Will I experience respiratory irritation during a Florida red tide?

Some people experience respiratory irritation (coughing, sneezing, tearing and an itchy throat) when the Florida red tide organism, K. brevis, is present and winds blow onshore. Offshore winds usually keep respiratory effects experienced by those on the shore to a minimum. The Florida Department of Health advises people with severe or chronic respiratory conditions, such as emphysema or asthma, to avoid red tide areas.

Is there a group of people who should avoid the beach during Florida red tide?

People with underlying chronic respiratory problems like asthma or COPD should avoid red tide areas, especially when winds are blowing toxins on or near shore, according to the Florida Department of Health.

Red tide seems to affect me even when I’m not right on the beach. Why?

Mote Marine Laboratory studies have shown that airborne red tide toxins can travel up to a mile inland, depending on the wind direction and other weather patterns. That means, even if you are a few blocks away from the beach, the toxins could still be affecting you.

I don’t have a chronic lung disease, but still seem to be affected by the toxins. I live near the beach. What should I do to lessen the effects?

Keep your windows and doors closed, keep the air conditioning or heat on and make sure you check or change the unit’s filter regularly.

What are some other health tips?

When driving, keep your car windows up and the A/C or heat on.
•    For people without asthma or any other chronic respiratory problems, over-the-counter antihistamines may relieve symptoms.
•    People with chronic respiratory ailments should be especially vigilant about taking prescribed medications daily.
•    If you do feel discomfort, you should also limit your outdoor activities — like golfing, tennis or bicycling — or do them away from the beaches during red tides.
•    Always seek medical care if your symptoms worsen.

Click here for current beach impacts, or go to
Click here for current red tide status updates, or go to
To report Fisk kill, please see

Can I swim in the ocean when there’s a Florida red tide bloom?

Swimming is safe for most people. However, the Florida red tide can cause some people to suffer skin irritation and burning eyes. People with respiratory illness may also experience respiratory irritation in the water. Use common sense. If you are particularly susceptible to irritation from plant products, avoid an area with a red tide bloom. If you experience irritation, get out of the water and thoroughly wash off. Do not swim among dead fish because they can be associated with harmful bacteria.

What are some hints for visiting beaches during Florida red tides?

Check the marine forecast, fewer red tide toxins will be in the air with offshore winds.
Check Mote’s Beach Conditions Reporting for conditions at the beach you plan to visit.
If you experience respiratory irritation, wear a mask, such as a painter’s mask, that covers the nose and mouth to filter out marine aerosol particles that contain the red tide toxins.
If you are asthmatic or have chronic lung disease, be vigilant about taking your prescribed medicines daily.  The state health department recommends that people with such diseases avoid beaches that are being affected by red tides 
Always seek medical care if your symptoms worsen.
For your home or motel room, keep your windows closed, the A/C on and check/change the unit’s filter.


Is it OK to eat shellfish at a restaurant or purchase shellfish from a seafood market during a red tide? (also known as commercially caught or store bought)

Yes. Store-bought and restaurant-served shellfish are safe to eat during a bloom because the shellfish industry is closely monitored by state agencies for shellfish safety. Commercially available shellfish are often not locally harvested and, if harvested locally, are tested for red tide toxins before they are sold. The Florida Department of Agriculture and Consumer Services closes shellfish harvest areas affected by Florida red tide.

Is it OK to eat recreationally harvested shellfish during a red tide?

No. Recreational harvesting of bivalve molluscs such as hard clams, oysters and mussels from conditionally approved or approved shellfish harvesting areas is banned during red tide closures; these organisms should not be harvested and eaten from any closed shellfish harvesting area to protect the public from neurotoxic shellfish poisoning (caused by eating red tide-contaminated seafood). To determine whether or not harvesting of shellfish is permitted in an area, visit the Florida Department of Agriculture and Consumer Services, Division of Aquaculture website. Edible parts of other animals commonly referred to as shellfish (crabs, shrimp and lobsters) are not affected by the red tide organism and can be eaten. Do not eat the tomalley (green stuff, hepatopancreas). During scallop season, locally harvested scallops from open scallop harvesting areas are also safe to eat as long as you eat only the muscle of the scallop and not the whole animal.

In addition, illegally harvested and unregulated shellfish are particularly dangerous and should never be consumed. For example, coquina clams and molluscan predators, such as whelks that feed on toxic bivalves, readily accumulate toxins in their tissues. An illegal harvest is a dangerous harvest.

Is it OK to eat local finfish during a red tide?

Yes, it is safe to eat local finfish as long as the fish are filleted before being eaten. Although toxins may accumulate in the guts of fish, these areas are disposed of when the fish are filleted. However, it is never a good idea to eat dead or distressed animals, especially in a red tide area, because the reason for the animal’s strange behavior or death cannot be absolutely known.

Does cooking or freezing destroy the Florida red tide toxin?

No, cooking or freezing does not destroy the Florida red tide toxins. Furthermore, the toxin cannot be seen or tasted.

Could Florida red tide affect my pets?

Just like people, pets may be affected by the Florida red tide. If you live close to the beach, consider bringing outdoor pets inside during a bloom to prevent respiratory irritation. If you are at the beach with your pets, do not allow them to play with dead fish or foam that may accumulate on the beach during or after a red tide. If your pet eats dead fish, it may get sick. If your pet swims in the red tide, wash it as soon as possible. Most dogs lick themselves after swimming and will consume any toxins on their fur.

Where can I get more health and safety information on harmful algae?

Centers for Disease Control and Prevention:
Florida Department of Health:
Health-related information/reporting of illnesses from exposure to red tide: call toll-free 24/7 Florida Poison Control Information Center at 1-800-222-1222.

Can we control or mitigate Florida’s red tides?

Currently there is no tried-and-true way to completely remove the Florida red tide algae and its impacts without potentially harming Gulf ecosystems. Mote scientists are studying control and mitigation methods that may benefit limited-tidal-exchange waterways, such as dead-end canals and small embayments in red tide-affected coastal communities.

The harmful effects of Florida red tide are caused by toxins released when the organism Karenia brevis dies. Potential controls must kill the red tide organism, eliminate the toxins from the water and avoid harming the ecosystem. Controls must also be practical. Red tides vary greatly in size – expanding as far as 10,000 square miles – and can be present from the surface of the water to the seafloor.

Over decades, scientists (including Mote scientists) have worked to rule out ineffective control and mitigation strategies and redirect attention toward more promising ones..

In the 1950s, U.S. Fish and Wildlife Service and State of Florida scientists used copper sulfate to attempt to eliminate a red tide in coastal Florida waters. Although the copper sulfate killed some of the red tide cells, it led to the release of toxins that, along with the copper sulfate, had negative effects on other marine organisms.

Mote Marine Lab worked with Woods Hole Oceanographic Institution to test the effectiveness of various clays for removal of red tide cells and toxins, and with appropriate permits, conducted several small-scale, pilot-test applications of clay in Sarasota Bay. The phosphatic clay by-product of phosphate mining was the most effective of those tested. The study demonstrated that the clay effectively removed red tide cells and toxins from the water under controlled laboratory conditions and in field tanks or mesocosms.  There was a measurable effect of the sedimented clay and its associated toxin on bottom-dwelling organisms, but those impacts were no worse than the impacts of the red tide itself.  In fact, it was difficult to find a ”control” site during the mesocosm field studies because virtually all life on the tested areas of ocean bottom had already been killed by the red tide.  Despite these promising results, project scientists concluded that phosphatic clay was not a good choice for local waters because of that specific clay’s undesirable properties (e.g., potential radioactivity, metal contamination, strong public concern about its use, etc.).  New studies led by Woods Hole with Mote partners will investigate a different clay substance to ascertain whether it is a more suitable red tide mitigation tool.

As of 2018, Mote is investigating multiple potential control and mitigation tools:

  • Ozonation (a patented process we already use to remove red tide in the water entering our public Mote Aquarium and the marine mammal and sea turtle hospitals) to be used to destroy red tide algae and their toxins in limited areas of water such as canals and small embayments.
  • “Living dock” structures covered with filter-feeding animals that remove red tide from limited areas of water such as canals and small embayments.
  • Concentrating naturally produced compounds from certain macro-algae (seaweeds) to be used to fight red tide blooms in the wild, considering that we know that these compounds can kill red tide in the lab.
  • Use of algae in the Amoebophrya genus (the same broader group as Karenia, the dinoflagellates) to serve as a natural control parasite for K. brevis red tide blooms

What can you do

In general we can each do our part to help keep our waterways clean.

Even though we don’t know everything yet about how human activity relates to a Florida red tide that has moved to shore, we know that there is the potential for coastal nutrients to influence blooms, and we certainly know that excess nutrients and other kinds of pollution flowing into our coastal ecosystems are generally bad for those systems and should be reduced.

One way that we can each reduce nutrients in storms water runoff is to choose yard plants that require less fertilizer, use slow release fertilizer and minimize fertilizer use overall.

There are more tips on how to keep waterways clean here.
For instance, be diligent about picking up pet waste.