Algae are tiny rootless plants that grow in water and are an important part of the marine food web. Most algae species are harmless. Harmful algae blooms, or HABs, occur when toxic algae species grow quickly and form clusters that make the ocean look red or brown. Algae blooms are sometimes called “red tide” or “brown tide.” 

Algae blooms can block the sunlight that other marine organisms need. Extremely large algae blooms can deplete the oxygen in the bottom waters of lakes, estuaries, and coastal environments. They can damage the fishing industry, shoreline quality, and local economies. 

Some algae species can produce toxins that are harmful to marine life, fish, animals, and humans, even causing death. People who eat shellfish contaminated by algae blooms may get food poisoning, sometimes very severe, and have respiratory problems. Local health departments issue warnings when harmful algae blooms occur. Follow their advice on shore and water activities and on shellfish safety.

This description is based on the information found in the Web links listed with this topic.

Web Links from MedlinePlus (National Library of Medicine)
Bacterial Infections
Foodborne Illness
Water Pollution

More Links
Algae Blooms (National Oceanic and Atmospheric Administration)
HABs and Marine Biotoxins (National Oceanic and Atmospheric Administration)
Harmful Algae Blooms: A Public Health Concern (Oregon Department of Human Services) (PDF — 3.6 MB)
Harmful Algae. Human Health (US National Office for Harmful Algal Blooms)
Harmful Algal Blooms (HABs) (Centers for Disease Control and Prevention)

Last Updated: October 16, 2012