After a couple weeks of reprieve, red tide is back in Southwest Florida. In case there’s any doubt, this is the same red tide bloom that’s been plaguing us since late October of 2017. It’s also the same bloom that is currently on Florida’s east coast, and likely the same bloom that’s up in the Panhandle.

Many people have been very confused about this year’s algal blooms. Unfortunately misinformation shared on social media and through news outlets has not helped the situation. I’ve seen maps showing red tide all the way up to the Peace and Myakka rivers. This never happened.

Another thing I’ve noticed is that as the media coined the term “red tide and algae crisis,” (the latter referring to the bloom in the Caloosahatchee) that many people began calling red tide bacteria. While blue-green algae is also called cyanobacteria, red tide is not a bacteria at all.

I thought it would be a good idea to spend some time discussing the difference between red tide and blue-green algae and where good, credible sources of information reside. None of this is simple, and it will take some time to educate yourself on the topic — but it’s time well spent.

What is red tide?

Red tides are caused by a type of algae — to be more specific, a plantlike organism called a dinoflagellate (die-no-FLADGE-uh-let). Dinoflagellates are microscopic and comprise approximately 2,000 species worldwide. Roughly 90 percent of all dinoflagellate species are marine. There are also freshwater dinoflagellates, including a few found in snow. Most dinoflagellates are harmless, but some, such as Florida red tide, are toxic.

While red tides can form around the world, the dinoflagellate that causes Florida’s red tide, Karenia brevis, is found almost exclusively in the Gulf of Mexico. K. brevis produces a substance called brevetoxin. It’s a neurotoxin (a poison that acts on the nervous system) which causes fish kills and may also cause the poisoning of humans when the toxins accumulate in the tissues of shellfish. Brevetoxin may also become airborne, causing respiratory irritation or distress in humans.

Scientists know that K. brevis blooms originate 10 to 40 miles offshore. Winds and currents bring them inshore, usually in bottom waters. K. brevis can use many different forms of nitrogen and phosphorus, and the sources of these nutrients may differ between the offshore, nearshore and estuarine environments.

What is blue-green algae?

Cyanobacteria, also called blue-green algae, are a group of organisms that can occur in fresh or salt waters. Like fish, most can live only in one or the other — few species can handle moving from salt to fresh water or vice versa. These organisms are naturally occurring in Florida’s environment and are also found all over the world.

Although we refer to it as an algae, cyanobacteria are actually far more primitive than true algae, having appeared 3.5 billion years ago. In fact, they were the first organisms to photosynthesize and produce oxygen in our atmosphere. There are 2,698 described cyanobacteria species. Although blooms of Microcystis and other cyanobacteria species are often lumped in with other harmful algae blooms (HABs), they are more accurately known as cyanobacterial HABs, or cyanoHABs.

Some species of cyanobacteria occur in the ocean, but blooms — extremely high levels that create surface scums of algae — happen mainly in lakes and rivers, where salinity is low. There are several different kinds of blue-green algae that can cause these blooms, including Microcystis, Anabaena, and Cylindrospermopsis.

Microcystis aeruginosa, the dominant species found in Lake Okeechobee this year, is known to release a toxin called microcystin. Microcystin can result in gastrointestinal problems and possibly liver damage in people if contaminated water is ingested. These toxins are also known to be lethal to cattle and domestic pets when they drink contaminated water or lick it from their fur after bathing in it.

Who is responsible for monitoring the red tide?

Many groups of scientists and volunteers work together to monitor and research HABs such as red tide throughout the year, regardless of a bloom’s presence. Water samples are collected from more than 100 locations throughout Florida on a weekly, bi-monthly or monthly basis through partnerships with state agencies, county governments, and citizens.

Collection sites are sometimes randomly selected by those conducting the sampling or taken from pre-selected locations that are visited frequently. The water samples are taken from the shore, bridges, piers, and by boat to track what is going on along the coast as well as in offshore waters where red tide originates.

This method of sampling allows the Florida Fish and Wildlife Conservation Commission, the agency who provides regular updates on HABs for the state of Florida, to cover a large area in a timely and cost-effective manner.

Once the water samples are collected, they are shipped to the Fish and Wildlife Research Institute where they are processed by biologists. Each sample is individually scanned for the presence of three harmful algal bloom species: K. brevis, Pseudo-nitzschia spp. and Pyrodinium bahamense, with other toxic species noted. If you want more info about these algae, try these links: K. brevis,; Pseudo- nitzschia,; Pyrodinium,

Where can I find up-to-date information on the bloom?

During periods of non-red tide blooms, full reports are posted each Friday by 5 p.m. on the Red Tide Current Status page ( The report is broken down by region and outlines the compiled data in both chart and map formations. Each chart details the location and date that the water sample was taken, the concentration of red tide cells present, and the agency responsible for collecting the sample.

The interactive Google Earth map is a more visual approach of the same information included in the chart report. Samples are displayed by location and are color-coded based on the concentration of red tide cells that were detected. Additional information about the sample is provided when the color-coded dot is clicked on. When available, a satellite map can be overlaid on the Google Earth map; however, during times of heavy rains the satellite maps are unavailable.

When a red tide bloom is active, additional reports in the form of interactive maps are provided by 5 p.m. daily at

What kind of sampling is done to track this bloom?

The University of South Florida’s College of Marine Science runs the Ocean Circulation Group, which models the transport of the bloom conditions at the surface and at the bottom of the water column. This interactive map allows visitors to click on their area of interest and view the best prediction of where the red tide is headed on the West Florida Shelf (

The starting point of each trajectory is depicted by an X and is followed by a squiggly line of where that water will be headed over the next three days. Each trajectory is color-coded using the same cell category concentration as the FWC interactive maps.

What other resources are available?

Harmful algal blooms are also tracked at the federal level, and NOAA has multiple sites for red tide information. Cell counts and bloom status reports are available through the Harmful Algal Blooms Observing System ( A new NOAA tool tracks respiratory conditions (

In addition to these reports, there is a website dedicated to keep up with local conditions that you can check before you head out: This collaboration between the University of South Florida and Mote Marine Laboratory assists the FWC with providing the public with information regarding respiratory irritation and fish kills associated with the red tide blooms. Citizen scientists can participate in the collection of this data by reporting the current conditions to 941-BEACHES (232-2437).

Finally, Florida Sea Grant has developed some great resources about the algae blooms affecting our coasts. A primer on harmful algae blooms: Frequently asked questions about the 2018 red tide bloom: Regular updates on the Lake Okeechobee algal bloom:

Betty Staugler is the Charlotte County extension agent for the Florida Sea Grant Program. She is active in many areas relating to boating, fishing, and watershed/coastal living. The Florida Sea Grant College Program supports research and education activities that help Florida’s shoreline communities, industries and citizens wisely use the state’s coastal and marine resources. Contact her at or 941-764-4346.


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