A harmful algal bloom. Image from the NPS "I Didn't Know That!" page on algal blooms
On a hot summer day you head for the water — and it looks off: discolored, a bad smell in the air, mat-like scum along the shore. That's likely a harmful algal bloom (HAB). You and your pets should stay out.
What a HAB is
Sun, warm water and extra nutrients make algae grow fast; a burst of growth is an algal bloom. Some algae are part of a healthy ecosystem — many animals eat them, and most species are harmless. But some are toxic to people, pets, wildlife and the environment, and when those bloom, it's a harmful algal bloom. HABs can occur in fresh water or salt water.
Thousands of HABs occur in U.S. waters every year, including in national parks, and they can harm fish, wildlife, pets, aquatic plants and people. Climate change and more runoff from lawns and farms have made them more frequent, in more places.
NPS photo
Staying safe
| If a HAB may be present | If a HAB is present |
|---|---|
| avoid contact with algae; take care with the water and rinse with clean water afterward | don't touch, swim in or drink the water; if you touch it, wash with soap and clean water |
| keep pets, children and livestock away from the water | keep pets away from the water |
| don't let pets or livestock drink the water or eat floating or dried algae | don't drink or cook with the water — boiling and filtering won't make it safe |
| throw away fish guts and rinse fillets in clean water before cooking; don't eat shellfish from the water | don't eat fish or shellfish from the water |
Either way: call your doctor or veterinarian if you or your pet get an unexplained illness or signs of poisoning after contact with algae, and report human illnesses to publichealthprogram@nps.gov. When in doubt, stay out!
Warning signs used where toxic algae may be, or is, present. Images from the NPS page on algal blooms
Helping prevent HABs
- Use less fertilizer, pesticide and herbicide on your lawn and garden.
- Plant native plants, which need fewer chemicals, are easier to keep alive and help pollinators.
- Pick up and properly dispose of pet waste.
The National Park Service's card on harmful algal blooms, for sharing. NPS
More in the series: I Didn't Know That!
Sources
Based on "I Didn't Know That!: Harmful Algal Blooms," National Park Service; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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