Florida Beach Guide to Red Tide

What is Red Tide?

Red tide is an out-of-control growth of algae. It is called by a microscopic single-celled organism called Karenia brevis. Red tide is almost always present in the Gulf of Mexico, but usually in small numbers. It often erupts into huge algae blooms when conditions are favorable, especially when fueled by water pollution. Human-generated pollution fuel red tide and make red tide grow rapidly. Common sources of pollution include industrial pollution, sewage, farm fertilizer and other sources.

Why is it called Red Tide?

Karenia brevis is commonly called “Red Tide” because it discolors ocean water into a rusty, dark red/brown color. Harmful algae blooms can also appear as other colors, including green and purple.

Where is red tide the worst in Florida?

Karenia brevis, the organism that causes red tide, primarily exists in the Gulf of Mexico. It can be found in all parts of Florida, including the Atlantic coast. Red tide spreads easily via ocean currents. Red Tide has been found as far north as North Carolina, although it originated in Florida waters.

What is Karenia brevis?

Karenia brevis is a microscopic microscopic plant organism. It produces neurotoxins that damage the central nervous systems of humans, pets, fish, birds, dolphins, manatees, sea turtles and many other living organisms.

The neurotoxins harm human health via respiratory exposure, physical contact and through the consumption of contaminated organisms, especially shellfish.

When waves crash on beaches they red tide neurotoxins can spread via the air, becoming “aerosolized”. Aerosolized neurotoxins can reach as many as four miles inland from a beach contaminated with red tide.

Red tide causes massive fish kills, marine mammal deaths, including dolphins and manatees, sea turtles and seabirds. Enormous whale sharks have also been killed by red tide. Dead fish release nutrients into the water, which further fuels the fire into a runaway outbreak growth cycle.

Red tide is harmful to the environment in a variety of ways. One of the worst knock-on effects of red tide is that it kills large beds of seagrass. Large algae blooms like red tide darken sea water which prevents sunlight from reaching grass on the seafloor.

Seagrass loss is devastating and has far-reaching effects for marine ecosystems. In recent years hundreds of manatees have starved to death due to seagrass due-offs. Many other species rely on seagrass as a nursery and breeding ground for juvenile organisms.

Fish kills further damage waterways because they release additional nutrients and deplete oxygen levels in the water, which in turn kills more marine life.

How long will the red tide last in Florida?

The length of a Red tide outbreak varies considerably. Red tide can last anywhere from a few days up to several months. In recent years some red tide outbreaks have become more intense. Some have lasted for up to 18 months. Red tide is heavily influenced by weather conditions, especially rain, wind and currents, which can increase or decrease the intensity and duration.

Is Red Tide natural? What Causes Red Tide?

Many people say that red tide is naturally occurring. This is partially true.

This message that “Red Tide is natural ” is often repeated by politicians, special interest groups and industrial polluters who want to avoid blame for water pollution.

It is true that Karenia brevis, the organism which causes Red Tide, is a naturally occurring organism. It usually lives 10-40 miles offshore in the Gulf of Mexico. It usually exists in small numbers which do not cause harm.

Large, harmful red tide blooms should not be thought of as “natural” because they are fueled by water pollution, which humans cause. Large-scale water pollution makes red tide much worse than it would ever “naturally” be.

Common sources of water pollution include:

  • Pollution from industrial phosphate mines
  • Untreated sewage from sewage treatment plants
  • Sewage leaks from old septic tanks
  • Animal sewage from industrial agriculture livestock
  • Fertilizer from industrial farming operations
  • Fertilizer from golf courses, yards and landscaping
  • Untreated groundwater
  • Vehicle and powerplant exhaust

Warming oceans due to climate change also contribute to harmful algae outbreaks, including red tide. Harmful algae blooms are becoming worse in terms of outbreak severity, and they are happening more often.

Red tide is only one form of harmful algae outbreak; other harmful algaes are also fueled by human causes, and also have destructive impacts on marine environments. Common examples include Sargassum seaweed, Blue-Green Algae and others.

Which Florida beaches have red tide?

Map of florida beaches affected by red tide
Image by Florida FWC

Red tide can affect all beaches in Florida, but it primarily affects beaches on Florida’s western coast and beaches along the Gulf of Mexico. Red tide can spread to Florida’s east coast. In 2018 many beaches were closed on Florida’s east coast, including beaches in Miami-Dade County, Palm Beach County and others.

This map from the Florida Fish and Wildlife Conservation Commission shows beaches which are currently affected by red tide.

Beaches along Florida’s central and southwest coast are most affected by red tide, including the beautiful beaches near Tampa Bay, Sarasota, Anna Maria Island, Sanibel and Captiva Island. Tampa Bay was impacted by an unusually severe outbreak of red tide in 2021 because of toxic water pollution discharged from the Piney Point gypsum stack, which is used to store contaminated industrial waste.

What is red tide season in Florida?

Low levels of Red tide are found in the Gulf of Mexico year-round, but harmful outbreaks follow a seasonal pattern. Red tide outbreaks usually occur in the late summer or early fall, when water temperatures are highest and when heavy rainfall washes nutrients and water pollution into the water. Red tides outbreaks can last through the winter and into the following spring. In recent years some red tide outbreaks have lasted for up to 18 months.

Red Tide Symptoms in Humans

Airborne exposure to red tide is dangerous, especially for people with asthma or breathing difficulties. Researchers have found that hospital admissions increased significantly when red tide is present.

Red tide is especially dangerous when molecules become aerosolized by wave action and sea spray. Aerosols contaminated with red tide toxins can be blown up to four miles in-shore from beaches.

Contaminated shellfish like mussels, oysters and clams are especially dangerous to eat because they accumulate red tide toxins.

For most people, red-tide causes severe respiratory irritation, coughing, sneezing and other symptoms which may resemble allergies. For a full list of symptoms, refer to the Center for Disease Control and National Institute for Health.

Why is red tide so bad in Florida?

Red tide negatively affects Florida for several reasons. Florida has warm water and ample sunlight which allows algae to grow quickly.

Florida has major problems with leaking sewer systems and septic tanks. These leaks introduce pollution and nutrients into Florida’s waterways. The nutrients act as fertilizer and cause algae to grow quickly, leading to outbreaks.

Discharges from polluted waterways, especially Lake Okeechobee, also contribute to red tide outbreaks. Lake Okeechobee is heavily polluted by industrial agriculture, animal sewage and sewage from poorly maintained septic, sewer and wastewater facilities.

Florida also has a large amount of pollution from groundwater runoff. When rain falls onto the ground it becomes groundwater. The groundwater flows across the ground and accumulates fertilizer, animal feces and other pollutants. The polluted groundwater then flows into storm drains, streams, rivers and eventually into the ocean, where the nutrient pollution fuels runaway algae growth.

Red tide is only one form of dangerous algae bloom in Florida; there are others, as well. While red tide afflicts salt water, another type of harmful algae called blue-green algae affects bodies of freshwater in Florida, especially lakes.

Blue-green algae is a major problem in Lake Okeechobee and fresh water systems in Florida. Blue-green algae has been linked to serious health problems for people who live near the water.

Blue-green algae has also threatened some freshwater drinking sources in Florida, prompting officials to warn citizens not to drink tap water in some situations.

How does red tide affect wildlife?

Red tide has killed huge numbers of fish, dolphins, manatees, sea turtles, sharks, birds, and even giant whale sharks. Pets can also be killed by toxic algae exposure.

Fish kills caused by red tide require massive clean-up operations to remove rotting carcasses. The stench from rotting animals is unbearable and can force residents to leave their waterfront homes, or avoid going outside.

Red tide also kills off seagrass, which is crucial for environmental health. This has caused a crisis in which hundreds of manatees have starved to death due to lack of seagrass. Seagrass destruction is a serious problem and causes a chain reaction of other environmental problems.

Can people swim in red tide?

Red tide is toxic to humans and causes numerous health hazards. People should not swim in water that is contaminated with red tide.

Exposure to red tide causes a variety of unpleasant and potential dangerous symptoms, including coughing, headaches, wheezing and many other symptoms. Skin exposed to red tide may become irritated.

People and pets should avoid swimming in water contaminated with red tide and should never swim near dead fish or other indicators of red tide.

Anyone who comes into contact with red tide or contaminated water should wash themselves immediately and thoroughly to remove any contamination.

Red tide is not fully understood and some health ailments may exist which are not yet known, including possible long-term neurological damage.

Can dogs be walked on beaches with red tide?

Dogs are vulnerable to numerous health effects from red tide. Dogs should not be allowed to come into contact with water which is contaminated with red tide, or to eat, access or play with sea foam, debris, dead fish or organisms which may be contaminated with red tide.

Dogs should be bathed thoroughly after swimming in water which may have red tide. Dogs often lick their fur to groom themselves after swimming, which may lead to accidental ingestion of red tide toxins.

How much does red tide cost taxpayers?

Red tide is hugely destructive for Florida’s environment. It is also costly for Florida’s economy in many ways.

Red tide causes mass interruptions to Florida’s tourist-driven economy. Restaurants, hotels, attractions and tours all suffer during red tide outbreaks. Interrupted tourism creates losses for the state of Florida due to lost tax revenue and due to long-term reputational damage.

Harmful algae outbreaks also threaten Florida home prices and Florida’s real estate industry because new residents are worried about future outbreaks.

Red tide cleanup operations are also extremely expensive and are generally impossible, due to the large-scale problem of red tide. It would be much better to control water pollution and avoid red tide in the first place.