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Harmful Algal Blooms (HABs)

What are Harmful Algal Blooms (HABs)?

Most algae are harmless and are an important part of the food web. Certain types of algae can grow quickly and form blooms, which can cover all or portions of a lake. Even large blooms are not necessarily harmful. However some species of algae can produce toxins that can be harmful to people and animals. Blooms of algae species that produce - or have the potential to produce - toxins are referred to as harmful algal blooms (HABs). HABs blooms most often occur in nutrient-rich waters, particularly during hot, calm weather.

Keep reading for an overview of HABS and how to keep you and your loved ones safe. Click on the links below for more detailed information.

Avoid Algal Blooms

Because it is hard to tell a HAB from other non-harmful algae blooms, it is best to avoid swimming, boating, otherwise recreating in, or drinking water with a bloom. DEC strongly recommend avoiding all contact with any floating mats, scums, or discolored water. It is not easy to tell by looking at it if a bloom will produce toxins or other compounds that can be harmful to human health or animals. Laboratory analysis of a water sample is needed to confirm the presence of toxins.

Before you go in the water, find out what waterbodies have blooms or have had them in the past. DEC maintains a HABs Notifications page of waterbodies that currently have blooms. Please note that if a waterbody is not listed, it does not mean that it does not have a bloom. It may have one that was not reported. Find out what waterbodies have had blooms in the past on the HABs Archive page.

Spilled paint appearance of an algal bloom.
Algae blooms may have the
appearance of spilled green paint.

Freshwater Blue-green Algal Blooms

Cyanobacteria (also known as blue-green algae), are naturally present in lakes and streams in low numbers. Cyanobacteria HABs are the most common type of blooms in New York. Sometimes, depending on environmental conditions, cyanobacteria can grow very quickly and produce blooms with high numbers of cells. Cyanobacteria can form blooms that discolor the water or produce floating scums on the surface of the water. HABs can reduce the recreational value of a waterbody, due to unpleasant appearances and odors. HABs cause a variety of ecological problems, such as reduced oxygen levels. The factors that cause cyanobacteria to produce toxins and other harmful compounds are not well understood.

Marine Algal Blooms

HABs can form in marine waters, producing marine blooms and a variety of biotoxin events that occur off the coast of New York and other eastern and coastal states. The DEC Bureau of Marine Resources has a Marine Biotoxin Monitoring Program to search for the presence of toxin-producing marine algae (Alexandrium and others) and to detect marine biotoxins in shellfish, such as clams, mussels and oysters.

What should I do if I see or come in contact with a bloom?

HABs may have the appearance of pea soup.
HABs may have the appearance of pea soup.
  • If you see it - avoid it
  • People, pets and livestock should avoid contact with water that is discolored or has algae scums on the surface. Colors can include shades of green, blue-green, yellow, brown or red. If contact does occur, rinse thoroughly with clean water to remove algae.
  • Never drink untreated surface water, whether or not algae blooms are present. Untreated surface water may contain other bacteria, parasites or viruses, as well as cyanotoxins that could cause illness if consumed.
  • People not on public water supplies should not drink surface water during an algal bloom, even if it is treated, because in-home treatments such as boiling, disinfecting water with chlorine or ultraviolet (UV), and water filtration units do not protect people from HABs toxins.
  • Stop using water and seek medical attention immediately if symptoms such as vomiting, nausea, diarrhea, skin, eye or throat irritation, allergic reactions or breathing difficulties occur after drinking or having contact with blooms or untreated surface water.
  • Please report any health symptoms to NYS Health Department at and your local health department (link leaves DEC website.)
  • For answers to other frequently asked questions go to the DEC HABs FAQ page.
  • If you suspect that you have seen a HAB or you, your family, or pet has been in contact with a bloom, please report the bloom to the DEC. Fill out and submit a Suspicious Algal Bloom Report Form (PDF, 763 KB).Email the completed form and, if possible, attach digital photos (close-up and landscape to show extent and location) of the suspected bloom to

What is New York State doing?

The DEC, the NYS Department of Health (DOH), and the NYS Office of Parks, Recreation and Historic Preservation (OPRHP) are working together to identify and respond to HABs concerns. DEC and DOH coordinate field personnel to investigate HABs reports. DEC and DOH are conducting research to learn more about HABs and to evaluate their risks to public health and the environment.

You may also contact your regional DEC office or contact:

DEC HABs Program Coordinator:
Rebecca Gorney, Ph.D., Division of Water
Phone: (518) 402-8179
Email the HABs Program

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