Harmful algal blooms are a major environmental problem in all 50 states. Red tides, blue-green algae, and cyanobacteria are examples of harmful algal blooms that can have severe impacts on human health, aquatic ecosystems, and the economy.

Algal blooms can be toxic. Keep people and pets away from water that is green, scummy or smells bad. 

• Learn about harmful algal blooms
  • Effects
  • Causes
  • What you can do
• See infographics, videos and other multimedia
• Find partner resources

Learn about harmful algal blooms

Harmful algal blooms can be green, blue, red or brown. They can be scummy or look like paint on the surface of the water.

What are harmful algal blooms?

Harmful algal blooms are overgrowths of algae in water. Some produce dangerous toxins in fresh or marine water but even nontoxic blooms hurt the environment and local economies.

What are the effects of harmful algal blooms?

• Produce extremely dangerous toxins that can sicken or kill people and animals
• Create dead zones in the water
• Raise treatment costs for drinking water
• Hurt industries that depend on clean water

Learn more about these and other effects.

What causes harmful algal blooms?

• Sunlight
• Slow-moving water
• Nutrients (nitrogen and phosphorus)

Nutrient pollution from human activities makes the problem worse, leading to more severe blooms that occur more often.

Learn where nutrient pollution comes from.

What you can do to help

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Volunteer to monitor waterbodies for algal blooms

• National Oceanic and Atmospheric Administration Phytoplankton Monitoring Network
• New York Citizens Statewide Lake Assessment Program
• Kentucky Watershed Watch
• Wisconsin Water Action Volunteers

Report suspected algal blooms to your state

State departments of health or environment are the best sources for local information about harmful algal blooms.

Find your state's contact information.

Help prevent nutrient pollution

Simple actions around your home and yard can make a big difference

Learn how you can help.

Multimedia

Infographics

Click to see full size.

Free webinars

See past webinars.

Videos

• Algal Blooms Can Harm Your Health
• Science safeguards drinking water from HABs
• Protect Your Pooch from HABs

Click to see more videos from EPA.

Blog

Keeping pets- and people- safe from toxic algae.
Two years ago, our family planned to take our Yellow Labrador puppy Fiona to Lake Needwood near our home in Rockville, Maryland for a swim. Read more...

Click to read other related blogs.

Photos

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Partner resources

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National resources

• North American Lake Management Society
• NOAA Harmful Algal Bloom Operational Forecast System
• Woods Hole Oceanographic Institute

State resources

• Florida Fish and Wildlife Conservation Commission Red Tide Status
• Florida Mote Marine Laboratory Beach Conditions Report
• Lake Erie Harmful Algal Bloom Bulletin
• Nebraska Department of Environmental Quality Toxic Blue-Green Algae Monitoring
• Ohio EPA Harmful Algal Bloom Advisories
• Oklahoma Department of Environmental Quality
• Oregon Health Authority Algae Bloom Advisories
• Texas Parks and Wildlife Golden Algae Status Reports
• Texas Parks and Wildlife Brown Tide Status Reports
• Vermont Department of Health Blue Green Algae Tracking
• Vermont Watershed Management Division

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