Red Tide (2023)

Created by Monica Bruckner, Montana State University

Red Tide (1)


The water in Penn Cove (Coupeville, WA) turned orange on 5/8/04 due to a "red tide." Photo courtesy of Mary Jo Adams (copyright 2004).

(Video) Dead fish litter beaches in Sarasota County as red tide persists

What is Red Tide?

Red tide is a phenomenon caused by algal blooms (Wikipedia definition) during which algae become so numerous that they discolor coastal waters (hence the name "red tide"). The algal bloom may also deplete oxygen in the waters and/or release toxins that may cause illness in humans and other animals. Species in the United States that release these harmful toxins include:

  • Alexandrium fundyense - found along the Atlantic coast from the Canadian Maritimes to southern New England
  • Alexandrium catenella - found along the Pacific coast from California to Alaska
  • Karenia brevis - found in the Gulf of Mexico along the west coast of Florida

What Causes Red Tide?

Major factors influencing red tide events include warm ocean surface temperatures, low salinity, high nutrient content, calm seas, and rain followed by sunny days during the summer months (NOAA). In addition, algae related to red tide can spread or be carried long distances by winds, currents, storms, or ships.

Where Are Red Tides Found?

Red tide is a global phenomenon. However, since the 1980s harmful red tide events have become more frequent and widespread. Detection of a spread is thought to be influenced by higher awareness of red tide, better equipment for detecting and analyzing red tide, and nutrient loading from farming and industrial runoff. Countries affected by red tide events include: Argentina, Australia, Brazil, Canada, Chile, Denmark, England, France, Guatemala, Hong Kong, India, Ireland, Italy, Japan, the Netherlands, New Zealand, Norway, New Guinea, Peru, the Philippines, Romania, Russia, Scotland, Spain, Sweden, Thailand, the United States, and Venezuela (WHOI, 2007, CDC, 2012).

How Are Red Tides Harmful?

Red tide algae make potent natural toxins. It is unknown why these toxins are created, but some can be hazardous to larger organisms through the processes of biomagnification and bioaccumulation. Grazers such as fish and krill are unaffected by the toxins, so as they eat the algae the toxins are concentrated and accumulate to a level that is poisonous to organisms that feed on them. Large fish kills and several mammalian diseases and deaths have been attributed to consumption of shellfish during red tide algal blooms. Diseases that may affect humans include:

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This Alexandrium species can cause paralytic shellfish poisoning. Image taken by David Patterson and Bob Andersen, provided courtesy of the microscope website.

  • Paralytic Shellfish Poisoning (PSP) - This disease is caused by the production of saxitoxin by the Alexandrium species. It is common along the Atlantic and Pacific coasts in the US and Canada. Poisoning occurs when one ingests shellfish contaminated with PSP toxins causing disruption of nerve function and paralysis. Extreme cases may result in death by asphyxiation by respiratory paralysis.

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This Dinophysis species can cause diarrhetic shellfish poisoning. Image taken by Mona Hoppenrath, courtesy of the microscope website.

  • Diarrhetic Shellfish Poisoning (DSP) - This disease is caused by the Dinophysis species. It generally occurs in Japan and Europe, but it has also been found in other countries such as Canada, the US, Chile, New Zealand, and Thailand. Symptoms of DSP include diarrhea, nausea, vomiting, abdominal pain, and cramps. DSP is generally not lethal.
  • Amnesic Shellfish Poisoning (ASP) - This disease, which has been found along the eastern Canadian coast, is caused by domoic acid producing planktonic and benthic algae, including Pseudo-nitzschia pungens forma. Pseudo-nitzschia multiseries and Amphora coffaeformis. It can also be found in soft shell clams and blue mussels infected by Pseudo-nitzschia delicatissima. Gastric and neurological symptoms include dizziness, disorientation and memory loss.

What is Being Done About Red Tide?

Technological advancements such as satellite imagery have allowed scientists to better track and monitor harmful algal blooms. Tracking and monitoring red tide algae helps reduce harmful effects of the algae by providing warnings against eating infected shellfish and against swimming in infected waters. For example, the Sarasota Operations Coastal Oceans Observation Lab (SO COOL (more info) ) has developed instruments that can test for red tide algae in coastal waters. Finally, researchers are attempting to develop an antidote to the red tide toxins. Interestingly, while developing such anti-toxins, researchers have found a possible cystic fibrosis (more info) treatment.

Red Tide Collections

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Photo by Miriam Godfrey.

General Collection Resources such as news articles, web sites, and reference pages provide a comprehensive array of information about red tide and other harmful algal blooms.

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Advanced Collection: Compiled for professionals and advanced learners, this red tide collection includes resources such as journal articles, academic reviews, and surveys.

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(Video) Red tide impacting Tampa Bay area beaches ahead of spring break

For Educators: This red tide collection includes activities, assignments, and reading materials created specifically for educators.

Additional Resources

For additional resources about red tide, harmful algal blooms, and related issues search the Microbial Life collection.


What are possible solutions to red tide? ›

Take a look at seven things you can do pretty much everyday to help.
  • Download a red tide reporting app. ...
  • Contact legislators. ...
  • Dispose of garbage properly. ...
  • Donate to research. ...
  • Choose your landscape well. ...
  • Be smart with your water. ...
  • Volunteer with a conservation group.
Apr 11, 2019

How long is red tide expected to last in Florida? ›

The bloom dissipated in the winter of 2018/2019. Red tides in Florida can last as little as a few weeks or longer than a year. They may even subside and then reoccur.

How far away can red tide affect you? ›

The first testing showed the blooms toxins can travel about three miles, making some people sick. “Coughing constantly, you feel like there is something in your throat,” said Sarasota resident Donna Zook.

Can you swim in water with red tide? ›

Most people can swim during red tide without serious risks, but it may cause symptoms such as skin irritation and a burning sensation in the eyes.

Can red tide be stopped? ›

Currently, there is no practical and acceptable way to control or kill red tide blooms according to FWC.

How do we get rid of red tide in Florida? ›

Clay mitigation involves spraying the surface of the water with a slurry of modified clay particles and seawater, and as the dense clay particles sink they combine with red tide cells. This process can kill the cells and also bury them in the sediment on the seafloor.

What months are the worst for red tide in Florida? ›

K. brevis blooms occur in the Gulf of Mexico almost every year, generally in late summer or early fall. They are most common off the central and southwestern coasts of Florida between Clearwater and Sanibel Island but may occur anywhere in the Gulf.

What year was the worst red tide in Florida? ›

Florida in 2018 and 2019 experienced one of the worst red tides in its history, lasting 15 months and causing respiratory infection outbreaks and leaving dead marine life along the southwest coast. A dead tarpon found in Pine Island Sound in August 2018. Red tide is a type of harmful algal bloom.

Can you swim in red tide Florida? ›

Don't swim in or around red tide because the toxin can cause skin irritation, rashes, burning and sore eyes.

Is it safe to walk on the beach during red tide? ›

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.

Can red tide get in your lungs? ›

Red Tide Can Cause Respiratory Issues; Lung Association Offers Tips to Protect Yourself. The red tide on the Gulf Coast of Florida doesn't just affect marine life, it can impact your lung health.

Can you cook red tide out of shellfish? ›

Toxic shellfish will taste and appear no different than nontoxic shellfish, and cooking does not destroy the red tide toxin. Testing is the only way to determine if shellfish contain unsafe levels of toxin.

Is rain good or bad for red tide? ›

Scientists speculate that rainfall could feed the harmful blooms that cause the red tides, thus rains help in prolonging the red tide phenomenon. A red tide is a phenomenon of discoloration of the sea surface. It is a common name for harmful algal blooms occurring along coastal regions.

Where is red tide the worst? ›

While many people call these blooms 'red tides,' scientists prefer the term harmful algal bloom. One of the best known HABs in the nation occurs nearly every summer along Florida's Gulf Coast.

Can you eat fish caught during red tide? ›

It is OK to eat local finfish during a red tide, with a catch. The Florida Fish and Wildlife Conservation Commission, or FWC, reports on its website that "yes, it is safe to eat local finfish as long as the fish are filleted before eaten."

Do humans make red tide worse? ›

However, certain human activities are making them more frequent. Chemicals from farming, factories, sewage treatment plants and other sources can become dissolved in water on the land. This water, called runoff, eventually flows into the ocean and can cause algae to grow faster, leading to red tides.

Can red tide make you sick? ›

Symptoms from breathing red tide toxins usually include coughing, sneezing, and teary eyes. For most people, symptoms are temporary when red tide toxins are in the air. Wearing a particle filter mask may lessen the effects, and research shows that using over-the- counter antihistamines may decrease your symptoms.

Does red tide smell? ›

With every breeze of wind that comes inland, the red tide brings a strong and disgusting smell of rot. What is this? The red tide smells like gone off food that is a long way into the decaying process, and it is enough to turn the stomach of anyone who smells it. This is because it has a very sulfurous scent.

Does Siesta Key have red tide? ›

People with severe or chronic respiratory conditions are advised to avoid red tide areas. Generally, symptoms are temporary.
Main Administrative Office.
LocationDateCell Count /mL
South Lido Park2/27/202360
Siesta Key2/27/202320
Turtle Beach2/27/2023160
Nokomis Beach2/27/202326
12 more rows

Where is red tide most common in Florida? ›

Red Tide is currently present in locations from the mouth of Tampa Bay to points south of Marco Island, from Pinellas County all the way south to Monroe County, towards the Florida Keys.
Common sources of pollution include:
  • Industrial pollution.
  • Human Sewage.
  • Agricultural sewage.
  • Agricultural fertilizer.
  • And other sources.
1 day ago

Can you eat seaweed during red tide? ›


Harmful algae are naturally occurring, but when they bloom into high concentrations they make shellfish toxic and unsafe to eat. These algae blooms are often referred to as “Red Tide” because they can turn the water a reddish brown color.

Does Clearwater Beach get red tide? ›

The latest report showed high levels of red tide at the beaches of Treasure Island, Redington Shores, Indian Rocks Beach and Sand Key Beach. Medium levels of red tide were detected at Pass-a-Grille Beach, Madeira Beach, Redington Beach, Clearwater Beach and Honeymoon Beach.

Is it safer to swim in the sea when the tide is in or out? ›

The safest time to swim in the sea is during a slack tide. A “slack tide” is when the water is most still. This means there is less water moving and currents are weaker. However, rip currents can still occur at slack tides so always stay aware of potential riptides.

Why am I coughing at the beach? ›

Offshore winds usually keep respiratory effects experienced by those on the shore to a minimum. “This is a chemical that has a reaction in the lungs. It produces a certain reaction in the cough mechanism that makes you cough.” It can make you sneeze as well.

Why does red tide make you cough? ›

The red tide also poses a health risk to people. The microorganisms emit brevetoxins, which can get blown into the air. When the toxins are breathed in, they constrict passages in the lungs, causing people to cough and have difficulty breathing.

Can kids get sick from red tide? ›

Most people may experience a mild cough or irritated throat, but for others, red tide could include eye irritation, sneezing, coughing, shortness of breath or even vomiting, particularly if your child has a respiratory condition like asthma.

What is the first aid of red tide poisoning? ›

The immediate first aid measure for red tide poisoning is the administration of baking soda. The patient must be brought to the hospital for further treatment. Activated charcoal is given to limit gastrointestinal absorption. Sodium bicarbonate and mannitol are given to enhance elimination of the absorbed poison.

Does cold weather help red tide? ›

2-Cold fronts can break up blooms

The organism that causes red tides here like warm, calm waters. Those conditions are typically found here in late summer and early fall, which is when blooms tend to form.

Do storms help red tide? ›

Red tide typically flares up when there's a persistent ocean current from the southeast. A storm can add to that coastward current, or it can reduce it.

Do hurricanes help red tide? ›

We have no evidence that a hurricane causes red tide,” said Michael Parsons, a professor of marine science at Florida Gulf Coast University and director of FGCU's Vester Marine and Environmental Science Research Field Station. “We don't influence their start, as far as we know.

Are Florida shrimp safe to eat? ›

Other shellfish seafood such as crabs, lobsters and shrimp can be eaten because they are not affected. Do not eat the tomalley (green stuff, hepatopancreas).

How long after red tide can you eat mussels? ›

These mollusks can accumulate a toxin called saxitoxin, which is produced by phytoplankton (dinoflagellates, diatoms and cyanobacteria). Some shellfish remain toxic for several weeks, while others can store the toxin for up to two years.

Is it safe to eat fish in Florida right now? ›

Florida's freshwater and marine fish are generally considered safe to eat.

How long will Tampa red tide last? ›

Red tides can last as little as a few weeks or longer than a year. They can even subside and then reoccur.

Is red tide present in Florida right now? ›

Is red tide present in Florida right now? Yes.

Is red tide happening more often? ›

Richard Stumpf, an algal blooms expert at the National Oceanic and Atmospheric Administration (NOAA), says red tides tend to occur in Florida every year. In Texas, they used to bloom every ten years, but now appear every three years.

Is red tide becoming more frequent? ›

Red tides have been around since long before humans. However, certain human activities are making them more frequent. Chemicals from farming, factories, sewage treatment plants and other sources can become dissolved in water on the land.

Can you swim in red tide Tampa Bay? ›

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.

Can a red tide outbreak last for more than a year? ›

Red tides in Florida can last as little as a few weeks or longer than a year. They may even subside and then reoccur.

What does red tide smell like? ›

The “sulfurous, rotten, decaying” stench has remarkable staying power as it wafts inland on sea breezes, Latz said. “I'm a mile and a half inland,” he said. “I smell it here.” Some kinds of red tide produce toxins that are harmful to sea creatures and humans, Latz said, but these events aren't poisonous, just putrid.

What Florida cities are affected by red tide? ›

Affected areas include beaches near St. Petersburg, Punta Gorda Beach, Stump Pass, Little Gasparilla Island, Boca Grande, Blind Pass, Marco Island, and others. Red Tide is also present at St. Pete Beach and others nearby, the northern and southern tips of Anna Maria Island, including at the entrance of Tampa Bay.

Does Clearwater Beach have red tide? ›

Medium levels of red tide were detected at Pass-a-Grille Beach, Madeira Beach, Redington Beach, Clearwater Beach and Honeymoon Beach. Low levels were detected at Fort De Soto Park and St. Pete Beach. At the last report, Fred Howard Park did not have measurable levels of red tide.

Do Hurricanes Get rid of red tide? ›

“During a hurricane or some other event that creates a lot of wave action, it will actually harm red tide, it'll break up the cells, and so it can reduce the bloom,”Parsons explained.

Why are red tides getting worse? ›

Florida's Red Tides Are Getting Worse and May Be Hard to Control Because of Climate Change - Inside Climate News.

How long after red tide can you eat shellfish? ›

Toxic shellfish are eaten, possibly making consumer sick in anywhere from minutes to 24 hours. With time the algae bloom dissipates so shellfish are no longer consuming toxic algae and eventually become safe to eat.

Why is there so much red tide in Florida? ›

Red tide in Florida and Texas is caused by the rapid growth of a microscopic algae called Karenia brevis. When large amounts of this algae are present, it can cause a harmful algal bloom (HAB) that can be seen from space.


1. Why is there red tide off Florida’s west coast?
(FOX 13 Tampa Bay)
2. Mote researchers: Clay could kill red tide without damaging environment
(FOX 13 Tampa Bay)
3. Ethnobotanist warns Tucker about the dangers of red tide in the Gulf
(Fox News)
4. What is Florida's red tide, and where does it come from?
(FOX 13 Tampa Bay)
5. Researchers: Red tide will get worse as it creeps up coast of Tampa Bay area's popular beaches
(10 Tampa Bay)
6. Here's how Tampa area experts can forecast red tide
(10 Tampa Bay)
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