Harmful algal blooms (HABs) are the rapid growth of algae that can cause harm to animals, people, or the local ecology.
A HAB can look like foam, scum, or mats on the surface of water and can be different colors.
HABs can produce toxins that have caused a variety of illnesses in people and animals. HABs can occur in warm fresh, marine, or brackish waters with abundant nutrients and are becoming more frequent with climate change.
Algae are a large group of plant-like organisms usually found in water.
They can vary in size from very small (microalgae) to very large (macroalgae) and can be found in all types of water, including marine (salt) water and fresh water.
Like plants, algae are essential to the earth because they produce the oxygen needed to sustain life.
Harmful algal blooms (also known as HABs) result from the rapid growth, or bloom, of algae that can cause harm to animals, people, or the local environment.
A harmful algal bloom can cause harm by:
Producing toxins that can poison humans, fish, seabirds, aquatic animals, livestock, wildlife, and household pets (such as dogs) that are near the water, drink the water, or swim in the water.
Causing illness when a person or animal eats fish or shellfish contaminated with algal toxins.
Becoming dense enough to keep sunlight from reaching the lower depths of the water.
Removing the oxygen from the water as it decomposes, starving fish and plants of oxygen, and damaging the local ecology.
What types of algae can become harmful algal blooms?
In salt water, harmful algal blooms may be called “tides” based on the color of the bloom. One example is Karenia brevis, an organism that forms the red tides sometimes seen in ocean waters along the Gulf Coast of Florida. Breathing in toxins from red tides can cause irritation of the throat and lungs.
In fresh water, such as lakes and rivers, harmful algal blooms are most commonly formed from cyanobacteria. Because of their color, they are often called blue-green algae. Although they are called bacteria, they do not cause infections in people. Instead they can harm people by creating toxic substances that people might breathe in or accidentally eat.
Harmful algal blooms are found in bodies of fresh water, marine (salt) water, and brackish water around the world. They occur in waters across the United States.
Marine water—All coastal states in the United States have experienced harmful algal blooms, including Hawaii and Alaska.
Harmful algal blooms in the U.S. and around the world have been associated with food poisoning.
Imported seafood has been implicated in a number of HAB-associated poisonings in inland areas.
Brackish water—Harmful algal blooms have been reported in brackish waters, including estuaries and coastal waters, in the United States.
If you see an algal bloom, stay out of the water and keep your pets out of the water.
You cannot tell if an algal bloom is harmful by looking at it, so it is best to be careful and avoid contact.
If you or your pets do go in water that has an algal bloom, wash yourself or your pets off immediately afterwards with tap water.
Do not let your pets lick their fur until you wash them off with tap water.
When visiting lakes, rivers, or beaches, check your local water conditions, and follow any advice posted by your state or local environmental health department online or near the water.
If you have concerns about the appearance, smell, or taste of the water, stay out of the water and contact your local park authority, environmental authority, or health department.
Symptoms can vary depending on the type of exposure and whether the harmful algal bloom was from fresh or marine water. The symptoms also depend on the amount and type of toxin and how long the person was exposed to the contaminated water or bloom.
Symptoms from exposure to red tide blooms, such as coughing and eye irritation, start as soon as people arrive at the beach and typically end when they leave.
Symptoms from exposure to other harmful algal bloom toxins may begin within hours of exposure and can last for a few days.
In some cases, people can also experience liver or kidney damage.
The long-term health effects of harmful algal blooms in people and animals remain unclear.
Because we are still learning about the long-term health effects, it’s important to take steps to keep people and pets safe, such as not going into water containing harmful algal blooms.
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