Illness and Symptoms: Marine (Saltwater) Algal Blooms

People can get sick and have symptoms.

Symptoms vary depending on the type of toxin the person was exposed to.

One of the most common types of harmful algal blooms in the United States is Karenia brevis blooms (also called Karenia brevis red tides) in the Gulf of Mexico. An algal toxin that is often produced during these blooms is called brevetoxin.

Breathing in sea spray or getting water containing brevetoxin on your skin can cause symptoms including:

• Respiratory irritation (coughing, sneezing)
• Shortness of breath
• Throat irritation
• Eye irritation
• Skin irritation
• Asthma attacks

Types of illness that can be caused by eating seafood contaminated with toxins from harmful algae:

• Ciguatera Fish Poisoning (CFP)
• Neurotoxic Shellfish Poisoning (NSP)
• Paralytic Shellfish Poisoning (PSP)
• Domoic Acid Poisoning and Amnesiac Shellfish Poisoning (ASP)
• Diarrheic Shellfish Poisoning (DSP)
• Azaspiracid Shellfish Poisoning (AZP)

For more information on signs and symptoms of illnesses caused by marine toxins, see the Diseases and conditions caused by eating seafood contaminated with algal toxins section below or visit CDC’s Yellow Book, Chapter 2: Food Poisoning from Marine Toxins.

If you think you may have symptoms caused by a harmful algal bloom in salt water, you can:

• Talk to your healthcare provider for advice about how to relieve your symptoms. Let them know that you might have recently come in contact with a bloom or its toxins. While there are currently no available tests or special treatments for illnesses caused by algal toxins, information about the suspected cause of your illness might help your healthcare provider manage your symptoms.
• Call your poison control center hotline at 1-800-222-1222. The specialists might be able to provide information about illnesses caused by blooms.
• Report any illnesses that you believe were caused by algal toxins to your local or state health department. This can help them understand and prevent harmful algal blooms and illnesses. Some state health departments have forms on their websites or hotlines for reporting suspected bloom-associated illnesses directly to the health department.

Animals can be poisoned by swimming in water with a marine harmful algal bloom or by eating fish or shellfish containing marine toxins. These toxins can build up in seafood through larger fish eating smaller fish. When animals are exposed, they can develop neurological damage or die within hours to days of swimming in unsafe water or eating seafood that contains toxins.

In marine mammals, fish, and other aquatic marine life, exposure to algal toxins can cause widespread illness or death. Animals can be poisoned in different ways and have different symptoms.

Fish

Fish kills (large die-offs of fish) can be caused by toxins called brevetoxins from blooms of the dinoflagellate (single-celled organism) Karenia brevis.

Mammals

Indian manatees can be poisoned by brevetoxins from blooms of the dinoflagellate Karenia brevis and may have fatal respiratory damage.

Dolphins can also be poisoned by this toxin, resulting in many animals stranded on beaches.

California sea lions can be poisoned by a toxin called domoic acid from blooms of the diatom (single-celled organism) Pseudo-nitzchia and experience neurologic effects, including seizures and unusual behavior.

Birds

Birds can get sick and die after eating algae or contaminated marine fish or shellfish. For example, pelicans and cormorants have been poisoned by these toxins. In some cases, thousands of birds died.

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 yourself and your pets safe, such as not going into water containing harmful algal blooms. Learn more about how to prevent exposure to harmful algal blooms.

Talk with your healthcare provider if you have questions about your health and exposure to a harmful algal bloom.