FAQs: Red tide vs blue green algae

Answers Provided by the Conservancy Environmental Science and Environmental Policy departments

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This is the most prolonged red tide event since 2006. Red tide was first detected in October 2017 and it has persisted off the Gulf Coast to varying degrees of intensity. Since the red tide event is still ongoing, it’s difficult to compare the wildlife and human impacts to other years. However, there has been a lot of reported respiratory irritation from humans, major fish kills, and many sea turtle deaths that are very likely linked to this red tide bloom.

Red tide is not always visible; when it is, there’s a reddish-brown tinge to the water. Other signs of red tide are coughing, eyes watering, throat irritation, trouble breathing, etc.

Blue green algae blooms, otherwise known as cyanobacteria blooms, are currently very visible in Lake Okeechobee, the Caloosahatchee River on the West Coast, and the St. Lucie River on the East Coast.

Red tide and blue green algae are two different types of algae blooms. Red tide (karenia brevis) occurs in marine waters, and blue green algae (cyanobacteria) in freshwater.

Blue green algae are naturally occurring, however, the introduction of excess nutrient pollution (from fertilizer, sewage, agricultural and stormwater runoff) from human activities cause cyanobacteria blooms to happen more frequently, last longer, and be more severe. Blue green algae blooms are not always toxic, but the one occurring now has tested positive for toxins that can be very harmful. Touching contaminated water can cause skin irritation and rashes, and ingesting it can cause gastrointestinal distress, and in some cases, liver damage. We strongly encourage anyone who sees water with a harmful algae bloom to avoid touching it, swimming in it, or fishing in it. We should also keep pets from coming into contact as well.

Red tide is also a naturally occurring phenomenon, however, this is the longest red tide we’ve had since 2006. Some studies have indicated that once red tide moves closer to the coasts, it can be fed by any sources of additional nutrients, including ones from fertilizer, sewage, or agricultural and stormwater runoff.

Bacteria/feces illnesses are different from the algae blooms, but they are related when they are caused by pollution runoff.

Pollution problems and algae blooms can happen year-round. For example, the red tide has been happening consistently since last October. The cyanobacteria blooms appear to be getting worse, and more frequent, due to continued nutrient pollution loading.

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It depends on the body of water, but generally, the water quality has been either staying the same or getting worse based on the pollutant lists from the Florida Department of Environmental Protection.

The Conservancy’s Estuaries Report Card can serve as a helpful guide to understanding the health of Southwest Florida’s rivers, estuaries and bays.

If you want to check the status of beaches:

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