Harmful Algal Blooms (HABs) in Parks’ Ponds and Lakes 

Each spring and summer, as temperatures rise and the days lengthen, algae become more common in New York City’s freshwater ponds and lakes. Most algae are harmless and are important parts of aquatic ecosystems, but some blooms produce toxins that pose a public health risk to people and animals if ingested or touched. It can be hard to tell the difference between Harmful Algal Blooms (HABs) and non-harmful algae, so it's best to avoid contact with any of our freshwater lakes and ponds.

Harmful Algal Blooms (HABs) are produced by naturally-occurring cyanobacteria in lakes and ponds. They can look like pea soup, a green paint spill, or thin blue or green mats floating on the surface or along the shoreline. HABs can cause skin and eye irritation from external contact, asthma-like symptoms from inhaling water/spray, and gastrointestinal and neurologic symptoms from ingestion. Children and pets are more vulnerable to these effects. Because blooms can be hard to identify, park visitors must avoid contact with any algae and heed all posted warning signs.

HABs dissipate when the chemistry balances or water cools — typically at the end of the summer seasons.

Tips for Avoiding Harmful Algal Blooms

Only some algae are harmful but it can be hard to tell the difference, so please avoid contact with any algae and observe the following guidelines: 

• Never drink from any of our lakes or ponds. 
• Never swim or wade in any of our lakes or ponds.
• Watch children at all times and do not allow them to enter or drink from lakes or ponds.
• Keep pets on leashes. 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 water affected by Harmful Algal Blooms, avoid further contact, rinse thoroughly 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.

More About Harmful Algal Blooms in NYC Parks

NYC Parks works with the New York State Department of Environmental Conservation (NYSDEC) and other partners to monitor water bodies for HABs. Confirmation of HABs is conducted through visual observation and photo verification by trained personnel. Signs are posted to inform the public where HABs are suspected or confirmed. Inspections have been regularly conducted at selected locations since 2016, following a larger evaluation of lakes and ponds.