NYC Resources311Office of the Mayor

Blue-Green Algae in Parks’ Lakes

Algae in Parks' water bodies become conspicuous as temperatures rise and days lengthen in spring and summer, and we see algae “blooms.”  These are usually seen as green-tinted water or carpet-like mats of floating green “pond scum” on some of our freshwater bodies. 

Algae are a widely varied type of plant life that range from single-celled microscopic organisms to giant kelp more than 100 feet long. Most algae are harmless and are important parts of aquatic ecosystems.

Blooms that produce blue-green algae (BGA) can be toxic.  BGA is technically not algae, but cyanobacteria. Some aquatic plants that look like algae or BGA are not.  Because it is difficult to tell the difference, assume you are seeing a BGA bloom when you see:

  • Water that looks like pea soup, or green, blue, or red paint.
  • Mats of blue or green pond scum floating on water surface or accumulated along the shoreline.

Park visitors must treat it cautiously, as BGA can be toxic. Children and pets are more vulnerable to its effects.  BGA can cause the following:                                        

  • Skin and eye irritation from external contact.
  • Asthma-like symptoms from inhaling water/spray.
  • Gastro-intestinal and neurological symptoms from ingestion. 

When enjoying fresh water features in city parks try to avoid contact with any algae and observe the following guidelines: 

  • Do not drink the water from these lakes or ponds.
  • Do not swim or wade in any of our lakes or ponds.
  • Watch children at all times near the shoreline and do not allow them to enter or drink from lakes and ponds.
  • Keep pets on leashes and do not allow them to enter or drink from lakes and ponds unless in areas specifically designated for such activities.

If you come in contact with or are exposed to BGA-affected water, avoid further contact, rinse with clean water and seek medical attention if symptoms such as skin, eye or throat irritation; allergic reactions or breathing difficulties; nausea, vomiting, diarrhea, dizziness, headache or fever occur.  Please report the symptoms to the New York City Department of Health and Mental Hygiene by calling  311.

Was this information helpful?