Go Back
  • For Business
  • |
  • Warnings
  • Data Suite
  • Newsletters
  • Advertising
  • Superior Accuracy™
52 dead, 27 girls at camp missing after catastrophic flooding in Texas. Read the latest Chevron right
Tropical Storm Chantal forms in Atlantic before landfall in South Carolina. Get details Chevron right

Columbus, OH

74°F
Location Chevron down
Location News Videos
Use Current Location
Recent

Columbus

Ohio

74°
No results found.
Try searching for a city, zip code or point of interest.
settings
Columbus, OH Weather
Today WinterCast Local {stormName} Tracker Hourly Daily Radar MinuteCast Monthly Air Quality Health & Activities

Around the Globe

Hurricane Tracker

Severe Weather

Radar & Maps

News

News & Features

Astronomy

Business

Climate

Health

Recreation

Sports

Travel

For Business

Warnings

Data Suite

Newsletters

Advertising

Superior Accuracy™

Video

Winter Center

AccuWeather Early Hurricane Center Top Stories Trending Today Astronomy Heat Climate Health Recreation In Memoriam Case Studies Blogs & Webinars

News / Weather News

What is red tide?

By Chaffin Mitchell, AccuWeather staff writer

Copied

As the worst red tide in more than a decade leaves hundreds of animals dead, here is what you should know to help you recognize toxic water the next time you visit the beach.

Before planning a visit to a southern U.S. beach, you may want to check if there is a toxic algae bloom invading the waters.

Red tide is a phenomenon that could ruin a beach visit by possibly irritating your respiratory system or making your eyes water. In addition to making beachgoers cough, it also contaminates shellfish and kills fish and larger marine animals, including dolphins and manatees.

"Red tide is a general term for harmful algal blooms (HABs) in the ocean. There are many different algae that are described as red tide," Dr. Richard Stumpf, oceanographer for National Oceanic and Atmospheric Administration's (NOAA) National Centers for Coastal Ocean Science, said.

These harmful algal blooms usually make the water reddish brown. Most of the red tide organisms are able to swim up and down in the water.

"Major red tide species in the U.S. Gulf of Maine red tide is Alexandrium fundyense, which is also found in Puget Sound and north into Alaska. The Gulf of Mexico red tide is Karenia brevis, and it has gone as far as North Carolina," Stumpf said.

Pacific Red Tide

An algae bloom creates a natural red tide. It is sometimes toxic and always organic. (PeakMystique/Getty Images/iStockphoto)

Stumpf noted that there is another algae species that makes water appear bright red, and these are not typically harmful.

Only rarely is the bloom so bad as to make the beach unusable.

"Normally, there are always beaches, days and times of day that are good. For example, under calm weather in the winter, the morning land breeze [wind blowing from land to ocean] makes the morning a better time to avoid the irritation," Stumpf said.

Alexandrium, a specific type of algae, lives in the sediment during winter. Once the temperature warms up in March and April, they pop out of the sediment. According to Stumpf, Alexandrium only rarely reaches concentrations dense enough to change the color of the water. The cells are quite toxic with saxitoxin, which is a potent toxin often known as paralytic shellfish toxin (PST).

Karenia brevis is always present at low concentrations in the Gulf of Mexico.

"If it reaches an area with more nutrients when the water is relatively calm, it grows. In the fall, changes in the wind patterns create upwelling on the Florida coast that, when combined with the swimming, accumulates Karenia at the coast," Stumpf said.

Karenia swim to nutrients or to light, depending on what it needs. If the right amount of nutrients and light meet in combination with the right ocean circulation, then a lot of cells can collect in a small area.

It doesn't always appear as a dark red and brown color, some algae like Karenia brevis can give a yellowish cast to the water when there are moderate concentrations.

In most cases, the highest risk comes from people consuming seafood that ate the toxin: for example, eating whole hard shellfish such as clams, mussels, oysters that have been collected in waters that are not tested.

"Dolphins in the Gulf of Mexico have died from eating small fish that are full of the toxin," Stumpf said.

Red tide fish kill

Massive fish kill caused by toxic harmful algae bloom, or red tide. (dombrowski/Getty Images/iStockphoto)

"Karenia brevis has brevetoxin, which affects nerves. It also affects fish gills, which causes them to die," Stumpf said.

According to Stumpf, if Karenia lasts into winter, it can settle on sea grass in warm water where manatees congregate to stay warm. Manatee illness and even sometimes death is common during blooms during cold winters.

People with asthma may need to use their medications after being around harmful algal blooms because the toxins can even become airborne.

"Brevetoxin is the one of the few toxins that can become an aerosol. It causes upper respiratory irritation, symptoms like a cold, immediately on exposure," Stumpf said.

After breathing the brevetoxin, it can reduce their lung function for hours to days after exposure.

"Healthy people recover rapidly," Stumpf added.

Red tide at the beach. Slight respiratory difficulty and plenty of dead fish. pic.twitter.com/YE14yZYX8N

— Leslie Anne Brooks (@lesliea_graham) February 11, 2017

"Most of the toxin blooms last weeks to months. Some Karenia blooms have persisted through an entire year [1995-1996, 2005]. A variety of factors will make the blooms end, and we don't understand this enough to predict when a bloom will end," Stumpf said.

Stumpf said they are able to look at a couple of indicators when trying to predict the bloom's end. The indicators include a lack of nutrients or disease of the algae due to a dense bloom favoring the spread of disease, a change to incompatible weather or the natural life cycle.

Before planning a trip to the beach, visit NOAA's tides and currents forecast. It provides an overview of the Gulf, forecasts, and links to state sites with more information.

<hr>

For more safety and preparedness tips, visit AccuWeather.com/Ready.

AccuWeather ready logo
Report a Typo

Weather News

Weather News

52 dead in Texas, 27 girls at Camp Mystic missing in flooding

Jul. 6, 2025
video

Rescuers save person clinging to an electric pole amid Texas floods

Jul. 4, 2025
Weather News

Record sargassum seaweed piles up on Caribbean islands, Gulf

Jul. 2, 2025
Weather News

Alabama teen in ICU after lightning strike hits boat, causing burns an...

Jul. 2, 2025
Show more Show less Chevron down

Topics

AccuWeather Early

Hurricane Center

Top Stories

Trending Today

Astronomy

Heat

Climate

Health

Recreation

In Memoriam

Case Studies

Blogs & Webinars

Top Stories

Weather News

52 dead in Texas, 27 girls at Camp Mystic missing in flooding

1 hour ago

Hurricane

Chantal to make landfall in South Carolina Sunday morning

2 hours ago

Severe Weather

Severe weather to rumble in the central US through the holiday weekend

10 hours ago

Severe Weather

Storms kill 3 in New Jersey, knock out power across Northeast

1 day ago

Weather Forecasts

Heat, humidity return to the East

11 hours ago

More Stories

Featured Stories

Weather News

Wildfires are tearing through a popular tourist hotspot in Greece

1 day ago

Weather News

‘Shark Whisperer’ swims its way into our shark obsession

1 day ago

Travel

Fourth of July gas hasn’t been this cheap since 2021

4 days ago

Weather News

What makes fireworks burst with vibrant colors?

1 day ago

Health

There is no safe amount of processed meat to eat, new research shows

2 days ago

AccuWeather Weather News What is red tide?
Company
Proven Superior Accuracy About AccuWeather Digital Advertising Careers Press Contact Us
Products & Services
For Business For Partners For Advertising AccuWeather APIs AccuWeather Connect RealFeel® and RealFeel Shade™ Personal Weather Stations
Apps & Downloads
iPhone App Android App See all Apps & Downloads
Subscription Services
AccuWeather Premium AccuWeather Professional
More
AccuWeather Ready Business Health Hurricane Leisure and Recreation Severe Weather Space and Astronomy Sports Travel Weather News Winter Center
Company
Proven Superior Accuracy About AccuWeather Digital Advertising Careers Press Contact Us
Products & Services
For Business For Partners For Advertising AccuWeather APIs AccuWeather Connect RealFeel® and RealFeel Shade™ Personal Weather Stations
Apps & Downloads
iPhone App Android App See all Apps & Downloads
Subscription Services
AccuWeather Premium AccuWeather Professional
More
AccuWeather Ready Business Health Hurricane Leisure and Recreation Severe Weather Space and Astronomy Sports Travel Weather News Winter Center
© 2025 AccuWeather, Inc. "AccuWeather" and sun design are registered trademarks of AccuWeather, Inc. All Rights Reserved.
Terms of Use | Privacy Policy | Cookie Policy | About Your Privacy Do Not Sell or Share My Personal Information

...

...

...