Algae are naturally occurring microscopic organisms that can be found in coastal and fresh waters. They can quickly grow out of control, or "bloom."

Most algae are not harmful, but some of these blooms produce toxins (poisons) that make people and animals sick. Symptoms can range from mild to life-threatening depending on the type of algae you come in contact with.

Harmful algal blooms can look like mats, foam, scum, or paint on the surface of the water. They can also grow underneath the water making them hard to see. The most common cause of harmful algal blooms in freshwater is due to Cyanobacteria (blue-green algae).

Although harmful algal blooms and mats have not been identified in the Fairfax Health District, they have been reported in other areas of Virginia and nearby jurisdictions. We encourage you to be aware of the water you enter.

Protect yourself, your family, and your pets from harmful algae.

• Do not swim or touch water that is discolored, murky, smelly, or has a film on the surface.
• Remember, when in doubt, stay out!

If you think you’ve seen or been in contact with a harmful algal bloom:

• Quickly rinse off with plenty of fresh, clean water.
• Report an algal bloom or a fish kill using the VDH Harmful Algal Bloom Online Report Form so it can be investigated.
• If you think you have symptoms caused by a harmful algal bloom, contact a doctor or the Poison Control hotline at 1-800-222-1222. Report health effects contact the HAB Hotline: 1-888-238-6154.
• Contact a veterinarian immediately if your pets seem sick after going in or near water. Animals can get very sick or even die within hours of coming into contact with harmful algae or cyanobacteria. Learn more about protecting animals.

Additional Resources

• Learn more about harmful algae from VDH and from CDC.
• Learn more about Healthy Swimming and Recreational Water Safety and see our Swimming in Natural Waters Advisory.
• Visit our web page and follow us on social media for updates on this and other health topics.