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FAQs About Harmful Algal Blooms (HABs)

Health & Safety Concerns

Q. The water in the lake is greenish. Should I stay out of the water? Should I report it?
Q. What should I do if a person I know has had contact with a bloom?
Q. Have there been any reports of illness caused by HABs in New York?
Q. What should I do if my pet or livestock animal has had contact with a bloom?
Q. I get my drinking water out of a lake. What should I be concerned about?

DEC's Notification System

Q. How do lakes get listed on the HABs Notifications page?
Q. If my lake isn't on the Notifications page, is it safe to swim in?
Q. Why are some lakes always listed? How does a lake get on (or off) of the Notifications page?
Q. Does the DEC close a lake if there is a bloom?

The Science of Harmful Algal Blooms (HABs)

Q. What causes HABs?
Q. Can the DEC predict HABs from year to year?
Q. What happens to HABs over the winter? Are there blooms under the ice?
Q. Why are some lakes more susceptible to blooms?
Q. I own a small private lake on my property. What can I do to prevent blooms?

Health & Safety Concerns

Q. The water in the lake is greenish. Should I stay out of the water? Should I report it?
A.
The greenish color may be caused by the presence of green algae or low levels of cyanobacteria (blue-green algae). Green algae do not produce harmful toxins; however it can be difficult to tell the difference between green algae and cyanobacteria (which can produce toxins and other harmful compounds). Visit the photo gallery web page to learn what green and cyanobacteria blooms look like. DEC recommends avoiding contact with any blooms, floating mats, scums, or discolored water. Any evidence of blooms should be reported to DEC using a Suspicious Algal Bloom Report Form.

Q. What should I do if a person I know has had contact with a bloom?
A.
Swimmers that have been in contact with HABs and experience any of the symptoms listed below should seek medical assistance.
The symptoms of HABs exposure for people include:

  • nausea, vomiting, diarrhea,
  • skin or throat irritation
  • allergic reactions or breathing difficulties

These symptoms are commonly mistaken for other gastrointestinal stress, whether from illness, food poisoning, or other health problems. Regardless of the cause of the illness, these symptoms may require medical attention. You should inform your physician and local health department if you were exposed to a HAB, both to help determine the proper course of treatment and to determine if others should be notified of this potential risk. More information about symptoms can be found on the Department of Health Blue-green Algae web page. (link leaves DEC's website)

Q. Have there been any reports of illness caused by HABs in New York?
A.
There have been a few reports of illnesses associated with HABs exposure, most of which have been minor. Since the symptoms from bloom exposure are very similar to symptoms from other gastrointestinal illnesses, we expect that bloom-related illnesses are under-reported. If you experience any of these symptoms after exposure to a bloom, please seek medical assistance from your physician and contact NYS Department of Health at harmfulalgae@health.ny.gov or your local health department.(link leaves DEC's website)

Q. What should I do if my pet or livestock animal has had contact with a bloom?
A.
HABs can be harmful to pets, or livestock. Large quantities of cyanobacteria cells can stick their fur and be ingested when the animal grooms itself. If exposed, rinse your dog, pet or livestock animal with clean water. Seek veterinarian medical assistance if your animal shows any signs of distress. HABs may release a fast-acting nerve or liver toxin that can be dangerous for pets, particularly dogs that swim within blooms. Your pet can start to experience symptoms within minutes to hours after being exposed to HABs.

The symptoms of HABs exposure for animals include:

  • Vomiting, diarrhea, loss of appetite
  • Excessive salivation or drooling,
  • Stumbling, seizures, convulsions, paralysis
  • Disorientation, inactivity, excessive tiredness
  • Fast heart rate, and difficulty breathing.

If you see or suspect any of these symptoms, particularly within 30 minutes to a few hours after exposure to an algae bloom, seek immediate veterinarian care. New York Sea Grant's Dogs and Harmful Algal Blooms (HABs) (806 KB, PDF) brochure has information about common dog symptoms, how dogs can be exposed to toxins, and how to reduce your dog's risk of exposure.

Q. I get my drinking water out of a lake. What should I be concerned about?
A.
Never drink untreated surface water, regardless of whether algae blooms are present. Untreated surface water may contain bacteria, parasites or viruses, as well as algal toxins that could cause illness if consumed. People not on public water supplies should not drink surface water, especially during an algal bloom. Even if the water is treated, in-home treatments such as boiling, disinfecting water with chlorine or ultraviolet (UV), and water filtration units do not protect people from HABs or toxins. If washing dishes in untreated surface water is unavoidable, rinse with bottled water to reduce possible residues. While we don't know if water containing low levels of HABs toxins could leave residues on dishes, taking this precaution may help reduce possible exposure risk.

DEC's HABs Notification System

Q. How do lakes get listed on the HABs Notifications page?
A.
Waterbodies are listed on the HABs Notifications page by DEC HABs Program staff when there is credible evidence of a current HAB. Reports on bloom occurrence can come from DEC staff, trained monitors, or the general public. If a bloom is suspected, a water sample may be collected and analyzed in an environmental testing laboratory. Lake residents and visitors should avoid exposure to any blooms, floating mats, scums, or discolored water, even at lakes not listed on the DEC HABs Notifications page.

Q. If my lake isn't on the Notifications page, is it safe to swim in?
A.
The waterbodies listed on the HABs Notifications page are based on information collected through DEC monitoring programs, regional HABs programs, and public reports. However, there are more than 7,000 lakes in the New York and most of these are not sampled routinely. There are risks associated with recreating outside of regulated swimming beaches, even in lakes that do not show up on the Notifications page. It is ultimately your own responsibility to decide if the risks associated with swimming in a lake are acceptable. Lake residents and visitors are reminded to avoid contact with floating mats, scums, discolored water or algae blooms- if you see it, avoid it!

Q. Why are some lakes always listed? How does a lake get on (or off) of the Notifications page?
A.
HABs may be short-lived (appear and disappear in hours) or long-lasting (persist for several weeks). The lakes that are "always" on the list may be blooms in multiple locations or have a persistent bloom. These lakes may be more susceptible to HABs based on high nutrient levels in the water or because of the lake's physical or land use characteristics. Some lakes are regularly posted on the Notifications page as a result of persistent blooms and active surveillance. Residents and visitors to New York state lakes should be aware that any lake can experience blooms and should avoid contact with blooms, floating mats, scums, or discolored water. If you suspect your lake has a bloom, please submit a Suspicious Algal Bloom Report form to HABsInfo@dec.ny.gov.

The HABs Notification page is updated every Friday, May through October. Sometimes there may be a short lag between when a bloom appears (or disappears) and when the lake is listed (or delisted) on the web page. Listings are moved to the HABs Archive page when a bloom is reported to be no longer visible or no new information was available to update the listing for three consecutive weeks.

Q. Does the DEC close a lake if there is a bloom?
A.
DEC does not have the authority to "close a lake" in the event of a bloom, although they can close beaches that are operated by DEC (generally limited to a small number of beaches within the Adirondack Park). Both the Office of Parks and Recreation local Department of Health has the authority to close swimming beaches. Beach operators close beaches as needed to assure public health and safety. This can happen under a number of circumstances, including when excessive algal blooms are detected.

The public should use the information on this site to help them to make informed decisions about where and when to recreate, particularly outside of designated swimming areas. Swimmers and recreational users should remember that health and safety cannot be assured outside of designated swimming areas- for more swimming information, visit DEC's swimming web page.

The Science of Harmful Algae Blooms (HABs)

Q. What causes HABs?
A. HABs are likely triggered by a combination of water and environmental conditions that, when aligned, allow cyanobacteria to out compete other algae. Environmental conditions may include: excess nutrients (phosphorus and nitrogen), lots of sunlight, low-water or low-flow conditions, calm water, and warmer temperatures. HABs may be short-lived, appearing and disappearing in hours, or long-lived, persisting for several weeks, depending on the weather and the characteristics of the lake.

Q. Can the DEC predict HABs from year to year?
A.
Some lakes regularly experience HABs during most summers. Lakes listed on the HABs Archive page for this year or previous years may be particularly susceptible to recurrent blooms in the future. Neither DEC nor researchers can accurately predict when or where blooms will occur. DEC collects and analyzes lake information to better understand why some lakes have blooms and others don't. The scientific community does not yet fully understand what triggers blooms or why some blooms produce toxins or other harmful compounds and others don't. Data collected in New York and other states continues to be studied to better understand HABs.

Q. What happens to HABs over the winter? Are there blooms under the ice?
A.
In most New York lakes, biological activity, including algae growth, is greatly reduced in the winter, as water temperatures fall and lakes ice over. Most algae growth decreases, although there are a few types of cyanobacteria that can grow in cold water, even under the ice. In rare cases, winter blooms have been reported in New York. Some HABs form overwintering spores that rest in bottom sediments and can cause blooms when water temperatures rise the following year.

Q. Why are some lakes more susceptible to blooms?
A.
Some lakes appear to be more likely than others to have frequent blooms. Excessive nutrients, particularly phosphorus, are probably the most important factors, but some lakes with relatively low nutrients still have blooms while some lakes with high nutrient levels don't have algae blooms. Preliminary results from studies conducted in New York and elsewhere suggest shallow lakes that repeatedly turn over during the summer, lakes with lower nitrogen to phosphorus ratios, and lakes with zebra mussels all may be more susceptible to HABs. Researchers continue to look at the characteristics of lakes with HABs in hopes of finding ways to minimize blooms.

Q. I own a small private lake on my property. What can I do to prevent blooms?
A.
There are a number of ways that lake residents can do their part to reduce the likelihood of HABs on their lake. Most of lake management actions are associated with the reduction of nutrients (phosphorus and nitrogen) added to your lake. The amount of nutrients can be decreased by: limiting lawn fertilization, maintaining septic tanks and shoreline buffers, reducing erosion and stormwater runoff, and maintaining water movement. Many of these nutrient control strategies are discussed in Chapters 7 and 9 in Diet for a Small Lake and in the Preventing HABs Section on the Information about HABs page.

Many of the nutrients inputs that can cause an algae bloom are associated with activities and sources outside of shorefront properties. Lake residents and lake associations should work together with local and county government agencies to identify sources of nutrients and identify strategies to reduce nutrient inputs to the lake. For more information, see DEC programs and resources to improve water quality.