Harmful Algal Blooms (HABs)

Beware of HABs: When In Doubt, Stay Out

HABs washing up on a shore of Cayuga Lake. Photo by the FLLT

Tompkins County Whole Health urges residents and visitors to beware of cyanobacteria blooms, also known as HABs (Harmful Algal Blooms). These blooms can occur in any calm body of water and may produce toxins that are harmful to people and animals. HABs have been observed at various locations in Cayuga Lake, including in Tompkins County, during the summers since 2017.

  • Do not drink the water and avoid contact with the water if it appears discolored or has an unpleasant odor.
  • Do not allow pets to swim in water with suspicious HAB blooms. 
  • Hot weather and intense rain and runoff events can lead to an increase in the presence of HABs.

HAB blooms may vary in size and while they may be confined to specific areas of the shoreline and bays, HABs are often transient (temporary), typically lasting only a few hours.

What Are HABs?

Several types of cyanobacteria can produce toxins and other harmful compounds that can pose health risks to people and animals through ingestion, skin contact, or inhalation. People recreating in and on the water should be aware of the potential for HABs in any waterbody they consider using. Because it is hard to tell a HAB from non-harmful algal blooms, it is best to avoid swimming, boating, otherwise recreating in, or drinking water with a bloom. Areas where blooms are not observed can continue to be used for recreational use.

Trained volunteers and local officials through the  Cayuga Lake Harmful Algal Bloom Monitoring Program (a collaborative of the Community Science Institute (CSI), Cayuga Lake Watershed Network, Discover Cayuga Lake and others) established to monitor much of the county shoreline for HABs on a weekly basis during the summer months. 

Note: There is no concern with municipal water supplies at this time. In the unlikely event that a public water supply is affected by HABs, the TCWH will work with the water supply to evaluate the situation and provide notice to affected users.

Know How to Identify HABs

Harmful Algal Blooms (HABs) might look like pea soup An image of toxic HABs off a boat dock. Courtesy Community Science Institute (CSI) An example of HABs. Courtesy Community Science Institute (CSI)

HABs come in many forms — from a green “spilled paint” sheen to thick pea soup, foam, or floating mats. Colors typically range from green to blue-green, but can also appear red or brown. If the water looks suspicious, keep people and pets away.
Non-Toxic Look-Alikes

Learn What HABs Look Like

If water appears discolored or has an unpleasant odor, do not drink the water and avoid contact with it.

  • Texture: Can look like spilled paint, pea soup, foamy scum, or thick floating mats.
  • Color: Most often green or blue-green, but can occasionally turn red or brown.
  • Location: Watch for accumulation along shorelines where waves push the mats.
  • To identify harmful and non-harmful algae blooms view a photo gallery.
  • View this video on YouTube for more information about identifying HABs.

Where Are HABs Now?

This is a map of the part of Cayuga Lake that's in Tompkins County. It shows locations of HABs along the shoreline during the summer of 2025

The Community Science Institute (CSI), Cayuga Lake Watershed Network, and Discover Cayuga Lake lead a volunteer program to monitor the Cayuga Lake shoreline for HABs during the summer months. Check for current HABs activity on Cayuga Lake using CSI’s interactive map.

“Blooms are often transient, typically lasting only a few hours. However, without testing, it is difficult to know if an area of water is safe to use. During these summer months, we urge the community to be aware, know what to look for, and avoid the area if it appears discolored or has an unpleasant odor.”
  — Doug Barnes, Senior Environmental Health Specialist

Get involved at CSI

  

IF YOU ARE planning to host a water event, please contact TCHD Environmental Health for guidance: 607-274-6688. Beaches may be closed due to the presence of HABs. Please contact individual facilities directly for more information.

HABs Are Toxic

  • If contact occurs with suspicious HABs, rinse thoroughly with clean water to remove cyanobacteria.
  • If you are not on a public water supply, be aware that water treatment such as Ultraviolet (UV), boiling, or chlorinating will not make your water safe for use.
  • Never drink, prepare foods, make ice, or cook with untreated surface water – whether or not a bloom is present.
  • 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.

Dogs Are At Risk

Prompt action is particularly important for dogs that may have gone in the water to prevent them from ingesting matter that sticks to their fur by self-grooming. Signs of toxin poisoning can occur within 30 minutes to a few hours after exposure, depending on the size of the dog and how much toxin the dog has ingested. If left untreated, cyanobacterial poisonings are usually fatal in dogs.

Pet Precautions

How can you reduce the risk of dog poisoning by cyanobacterial toxins?
  • A yellow lab dog, wading in water up to its chest and carrying a very large stick
    If possible, keep your dog on a leash near shorelines.
  • Don’t let dogs wade, drink the water or eat/walk in beach debris.
  • If your dog goes in the water please remove them immediately.
  • Don’t let them lick their fur or paws after getting out of the water.
  • Rinse/wash them thoroughly with fresh water from a safe source if available. (i.e. bottled water or household garden hose). Otherwise a towel or rag can be used to remove algal debris.
  • Use rubber gloves during pet cleaning, if possible.
  • Dry them thoroughly with a clean towel or rag.
  • Wash your hands with fresh water.
  • Look closely for any symptoms described.
  • Please notify the public health department or state natural resource management agency if you observe a suspected HAB.
  • Sea Grant NY logo
    More information on the risks HABS present to dogs from Sea Grant New York's Protect Your Dog From Harmful Algae(PDF, 1MB). 
     
    

For emergencies, contact the Cornell Veterinary Emergency Hotline: 607-253-3060.

If it might be a HAB, report it

If you see a suspicious bloom, stay out of the water and report the sighting. Trained volunteers will follow up to determine if it is or is not a HAB

These are NOT HABs

This is NOT HABs, it is Duckweed. Photo courtesy Community Science Institute (CSI) This is NOT HABs, it is Watermeal. Photo courtesy Community Science Institute (CSI)  

The images above show non-toxic look alikes. They do not contain HAB toxins, though heavy pollen or stagnant organic matter can sometimes irritate sensitive skin or eyes. Click the following links to open a collage of images: Algae(PDF, 199KB), Watermeal(PDF, 220KB), Duckweed(PDF, 198KB), Pollen(PDF, 196KB).

 

Additional Resources

Volunteer | Get Updates

  • Are you interested in becoming a HABs Monitoring Volunteer next season? Sign up here and you will be contacted in early spring 2027.
  • If you'd like to receive Cayuga Lake HAB Updates, subscribe to the Cayuga Lake Watershed Network's weekly newsletter.
Horizonal logo for CSI, the Community Science Institute in Ithaca  |  Logo for the Cayuga Lake Watershed Network. It's a circle with an illustration showing waves, the sun, and a goose flying

 

6/17/2026

Back to top