D E C banner
D E C banner


The New York State Department of Environmental Conservation has added a link to a translation service developed by Microsoft Inc., entitled Bing Translator, as a convenience to visitors to the DEC website who speak languages other than English.

Additional information can be found at DEC's Language Assistance Page.

FAQs About Blue-green Algae

DEC has received the following questions about blue-green algae blooms.

Health Concerns

Q. The water in the lake is greenish, but it doesn't look like any of the pictures on the DEC website. Should I stay out of the water? Should I report it?

A. The greenish color may be due to the presence of green algae or low levels of blue-green algae. Green algae do not produce harmful toxins; however it can be difficult to tell the difference between green algae and blue-green (toxic) algae. Visit the photo gallery web page to learn what green and blue-green algae can look like.We recommend avoiding contact with any floating rafts, scums or discolored water. Any of these conditions--discolored water, surface scums, or other evidence of blooms--should be reported to DEC. Report a suspicious bloom.

Q. If I swam in a lake before I was aware it had a blue-green algae bloom, what should I do?

A. Swimmers exposed to blue green algae blooms should seek medical assistance if they observe any symptoms associated with blue green algae toxins, from gastrointestinal illness to skin irritation. More information about these symptoms can be found on the Department of Health Blue-green Algae web page (see "Links Leaving DEC's Website") and the blue-green harmful algal bloom web page. These symptoms should also be reported to the county or regional health department. Pets should be rinsed with clean water after exposure to any blooms, and any unusual symptoms should be reported to the veterinarian.

Q. Are blue-green algae blooms harmful to dogs, pets or livestock? What should I do if my dog, pet or livestock comes in contact with a blue-green algae bloom?

A. Yes, blue-green algae can be harmful to dogs, pets or livestock. The blue-green algae cells can stick their fur and become concentrated when the animal cleans itself. Rinse your dog, pet or livestock animal with clean water and seek veterinarian medical assistance should your pet show any signs of distress.

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 o toxins, and how to reduce your dog's risk of exposure.

Q. If my lake isn't on the list, is it safe to swim?

A. The waterbodies listed on the notification web page are based on information from 150-200 lakes collected through DEC monitoring programs and public reports. However there are more than 7000 lakes in the state, and most of these are not routinely sampled.

There are risks associated with recreating outside of regulated swimming beaches, even in lakes that do not show up on this notification list. It is ultimately your responsibility to decide if the risks associated with swimming in a lake are acceptable. Lake residents and visitors are reminded to avoid contact with discolored water- if you see it, avoid it.

DEC encourages the public to report suspected blooms.

Q. I get my drinking water out of this lake, what are my concerns?

A. 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 algal toxins, that could cause illness if consumed. People not on public water supplies should not drink surface water, even if it is treated, during an algal bloom because in-home treatments such as boiling or disinfecting water with chlorine or ultraviolet (UV) or water filtration units do not protect people from blue-green algal toxins. If washing dishes in untreated surface water is unavoidable, rinsing with bottled water may reduce possible residues. While we don't know if water containing low levels of blue-green algal toxins could leave residues on dishes, taking this precaution may help reduce possible exposures.

Q. Have there been any reports of illness?

A. There have been a few reports of minor illnesses associated with blue green algae exposure. Since the symptoms from bloom exposure are very similar to symptoms from other gastrointestinal illnesses, we expect that blue-green algae related illnesses are under-reported. If you experience any of these symptoms after exposure to a blue green algae bloom, please seek immediate medical assistance from your physician and contact your local health department.

DEC's Notification System

Q. Why are some lakes always on list?

A. Blue-green algae blooms may be short-lived (appear and disappear in hours) or long-lasting (persisting for several weeks). The lakes that are "always" on the list may be experiencing multiple blooms or have a persistent bloom. These lakes may be more susceptible to blue-green algae blooms based on very high nutrient levels or the lake's physical and land use characteristics. However, some lakes also regularly show up on the notification list due to very active surveillance and a heightened awareness by the lake residents and the lake monitors. Residents and visitors to New York state lakes should be aware that any lake can experience blue green algae blooms, and should avoid direct contact with any discolored water.

Q. How do lakes get listed on the DEC website?

A. Lakes are listed on the DEC notification web page when there is credible evidence of a blue green algae bloom. This can come from visual evidence or water quality testing conducted by trained monitors. Lake residents and visitors should always avoid exposure to discolored water, even at lakes not listed on the DEC notification web page.

Q. My lake is listed on the DEC blue-green algae notification web page, but I don't see any blooms. What does this mean?

A. Blue-green algae blooms may be short-lived, appearing and disappearing within hours, or long-lasting, persisting for several weeks. They can also move throughout the depth of the lake and across the surface of the lake. It is difficult to predict how long a blue-green algae bloom will remain on a lake.

Because the web page is updated on Fridays, sometimes there may be a lag between when the lake bloom is no longer visible and when the lake is listed on the web page. For the most current information about any lake on the list, you should contact the Division of Water at 518-402-8179.

Public Concerns

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 algae blooms on their lake. Most of these lake management actions are associated with reducing 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.

Many of the nutrients inputs that can cause an algae bloom are from activities and sources outside of shorefront properties. Lake residents and lake associations should work with local and county government agencies to identify sources of nutrients and identify strategies to reduce nutrient inputs to the lake.

The Science of Blue-green Harmful Algae Blooms (HABs)

Q. What happens to blue-green algae over the winter? Are there blooms?

A. In most New York lakes, biological activity, including algae growth, is greatly reduced in the winter, as water temperatures decrease and lakes ice over. Most blue-green algae growth also decreases, although there are a few blue-green algae species that can grow in cold water and even under the ice. In rare cases, winter blooms have been reported. Some blue-green algae species form overwintering spores that can rest in bottom sediments and can cause blooms when water temperatures rise the following year.

Q. Can DEC predict blue-green blooms from year to year?

A. Some lakes regularly experience or may be susceptible to blue green-algae blooms. Lakes listed on the Archived Notices web page may be particularly susceptible to blooms in the future.

DEC cannot predict when or where blue-green algae blooms will occur. DEC is collecting and analyzing lake information to better understand why some lakes have blooms and others don't. The scientific community studying blue-green algae blooms does not yet fully understand what triggers blooms and why some blooms produce toxins and others don't. Data collected in New York and other states continues to be studied to better understand these blooms.

Q. 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, and some lakes with high nutrient levels don't have blue-green algae blooms. Preliminary results from studies conducted in NY and elsewhere suggest small, shallow lakes that repeatedly turn over during the summer, lakes with lower nitrogen to phosphorus ratios, and lakes with zebra mussels may be more susceptible to blue-green blooms. However research continues to look at the characteristics of lakes with blue-green algae blooms in hopes of finding ways to minimize these blooms.