Harmful​ Algae Blooms    

What are Harmful Algae Blooms?

Algae are microscopic plant-like organisms found throughout nature.  They occur in fresh, brackish and salt water.  When conditions are right, such as sunlight, nutrients, nitrogen, phosphorous, and the right salinity, algae may grow very quickly, forming visible blooms.  

Where do Harmful Algae Blooms occur?

In Maryland, algae blooms of all kinds can be found in the Chesapeake Bay, in rivers, ponds, lakes, creeks, and in the ocean.  

Are all algae blooms harmful?

Not necessarily.  Some can damage the environment by blocking sunlight.  Some can harm fish and plants by removing oxygen from the water, but those do not produce toxins that affect people and animals. 

What are the effects of Harmful Algal Blooms?

There are many types of algae, some can create toxins that cause harm to, aquatic life (plants, and fish), animals, and humans.

Animals are often affected and may become ill with symptoms of weakness, difficulty breathing, convulsions, or even death.  If you think your pet may be sick because of a harmful algal bloom, consult your veterinarian immediately.

What should I do if I suspect a Harmful Algae Bloom? 
Report algae blooms directly to
  • MDE hotline at 866-MDE-GOTO 866-633-4686 or  
  • DNR fish health hotline at 877-620-8367

For more information about health concerns, contact
  • MDH Environmental Health Helpline at 866-703-3266 or 
  • E-mail: mdh.envhealth@maryland.gov​​​ ​

For more information about Harmful Algae Blooms visit:

Maryland Deparment of the Environment 

Maryland Health Beaches Program

Maryland Department of Natural Resources 

Centers for Disease Control and Prevention 

American Veterinary Medical Association (AVMA)