Harmful Algal Blooms, or HABs, are a growing concern for Seneca Lake and many freshwater bodies across New York State. These blooms are often caused by cyanobacteria, also known as blue-green algae. Though they are not true algae, cyanobacteria are naturally occurring bacteria that use sunlight to create food through photosynthesis.
Under certain conditions—especially during the warm, calm days of late summer and early fall—cyanobacteria can multiply rapidly, forming dense surface blooms. These blooms can look like green or blue paint, pea soup, or floating mats.
Some cyanobacterial blooms produce toxins that are harmful to people, pets, and wildlife. The only way to know if toxins are present is through laboratory testing. Because of the health risks, HABs are closely monitored on Seneca Lake each season, with efforts focused on volunteer reporting, scientific confirmation, and public advisories.
What Are HABs?
HABs occur when conditions like warm temperatures, sunlight, and excess nutrients—especially phosphorus—promote the rapid growth of cyanobacteria. Not all blooms are toxic, but when toxins are present, they can affect drinking water, recreation, and overall lake health.
How We Monitor
Seneca Lake Pure Waters Association coordinates a volunteer-based monitoring program from July through October. Our trained HABs Spotters submit reports when they see blooms, helping us track where and when HABs occur. This data is shared with the New York State Department of Environmental Conservation (DEC), which manages the state’s official HABs reporting system.
How to prevent cyanobacteria blooms?
- Use phosphorus-free fertilizer.
- Maintain your septic system.
- Minimize stormwater run off.
- Properly dispose of chemicals.
- Create natural areas with native plants, bushes and trees.
Support HABs Monitoring on Seneca Lake
Your donation helps fund testing, volunteer training, and public alerts that keep our community safe from harmful algal blooms. Every gift protects clean water.
Text Alerts
Sign up to receive real-time text notifications whenever a harmful algal bloom is confirmed on Seneca Lake—you’ll get one message per event. To unsubscribe at any time, just reply STOP.
Monitoring HABs is crucial because it helps raise awareness of potential health risks, while also providing valuable data that supports long-term efforts to reduce nutrient pollution and improve overall water quality. By tracking when and where HABs occur, we can better understand their causes and work toward effective solutions.
2025 Bloom STATUS & Map
Legend:
- Dark Dots: Newer reports
- Light Dots: Older reports
- Gradient Effect: As time passes, dots fade from dark to light
HABs 101: What You Need to Know and How You Can Help
What do blooms look like?
Cyanobacteria blooms can be blue, bright green, or brown—they may look similar to spilled paint, pea soup, or greenish colored particles floating on the water’s surface.
What are the health risks?
Cyanobacteria blooms can be toxic and may cause health problems for both people and animals! Exposure can occur by touching, ingesting, or even breathing contaminated water (or vapor).
Exposure to cyanotoxins may cause an allergic reaction, breathing difficulty, headache, rash, stomachache, vomiting, diarrhea and even possible liver or neurological damage.If exposed individuals are experiencing adverse symptomsthey should seek immediate medical attention.
How to stay safe?
- People and animals should keep away from blooms in surface waters.
- Do not swim, wade, boat, fish or eat fish caught from areas near blooms.
- Never drink, prepare food, cook or make ice with surface water during a bloom.
- Boiling the water will not remove cyanobacteria or their toxins.
- Even if you have an in-home treatment system, use bottled water during a bloom.
- During a bloom you may consider not showering, bathing or washing, especially if your water looks cloudy.
- Potable water is always the best option for drinking, preparing food, cooking, or making ice, as well as, washing and bathing.
What You Can Do
Ready to make a real impact? Join our volunteer team to monitor shorelines, drive our communications, collect vital HABs data, and rally fellow volunteers in protecting Seneca Lake.
If you observe a suspicious bloom on Seneca Lake—such as discolored water, surface scum, or green paint-like streaks—it’s crucial to report it promptly to help protect public health and the lake’s ecosystem.
How to Report a Suspicious Bloom
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Avoid Contact: Keep people and pets away from the area.
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Document the Bloom: Take clear photographs of the bloom and note the exact location.
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Submit a Report:
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To the New York State Department of Environmental Conservation (NYS DEC): Use the online reporting form to provide details and upload photos.
- If you are would like us to take a look: Email your observations and photos to senecahabs@senecalake.org. We will do our best to respond in a timely manor.
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What Happens Next
The DEC will review your submission. Confirmed blooms are added to the NYS DEC HABs Map
Blooms reported by our observers can be found at Seneca Lake HABs Map & Current Bloom Chart.
If you see a suspicious bloom—discolored water, surface scum, or green paint-like streaks—stay out of the water and keep pets away.
Even if a bloom isn’t confirmed as toxic, assume it could be harmful. Exposure can cause skin irritation, nausea, or more serious health effects for humans and animals.
When in doubt, stay out. Never drink, cook with, or wash with water where a bloom is suspected. If contact occurs, rinse with clean water immediately and seek medical or veterinary attention if symptoms occur.
The best protection is awareness and avoidance.
Over the past eight years, Seneca Lake Pure Waters Association, the Finger Lakes Institute (FLI), and the New York State Department of Environmental Conservation (NYS DEC) have been working together to raise awareness, collect and analyze bloom samples, and notify the public of harmful cyanobacteria blooms on Seneca Lake.
Cyanobacteria, commonly known as blue-green algae or harmful algal blooms (HABs), thrive in calm, nutrient-rich waters and are found worldwide. Some species produce toxins that can negatively impact the health of animals and humans—making public notification critical.
In 2021, more than 120 volunteers monitored 60 miles of Seneca Lake’s shoreline, submitting weekly reports. That season saw more blooms than 2020, but far fewer than in 2019. Blooms began appearing in mid-August, mostly on the southeast side, and remained sporadic until October 6th, when a widespread, dense bloom covered much of the Finger Lakes. What causes a bloom to occur on one day but not another is still not fully understood.
Volunteers report both “bloom” and “no bloom” conditions using an online reporting system, which is also used by the Canandaigua Lake and Keuka Lake Associations. Only Seneca Lake bloom data is shown on the map on this page. For updates on those neighboring lakes, please visit their respective organizations.
When volunteers find a bloom, they take a photo and submit it as evidence. Even though sampling was not conducted in 2020 or 2021—due to the DEC pausing its program and COVID-related funding limitations—Pure Waters remains confident in the accuracy of bloom assessments. Trained volunteers have demonstrated more than 90% accuracy in identifying blooms, and previous years’ analysis confirms that most identifiable HABs are toxic. As a result, all visible blooms should be presumed toxic and avoided.
|
Year |
# Samples Analyzed |
# Confirmed HABs |
# HABs with High Toxins |
| 2022 | N.A. | 49 | N.A.^ |
|
2021 |
N.A. | 72 | N.A.^ |
| 2020 | N.A. | 15 | N.A.^ |
|
2019 |
96/40* |
86/40* |
34 of 40* |
|
2018 |
41 |
39 |
36 |
|
2017 |
60 |
50 |
22 |
|
2016 |
12 |
5 |
2 |
|
2015 |
9 |
5 |
1 |
|
2014 |
9 |
0 |
0 |
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NYS DEC HABs Map
View confirmed blooms statewide in near real-time:
https://www.dec.ny.gov/chemical/83310.html -
Bloom Status on Seneca Lake
Our trained HABs Spotters report suspicious blooms July–October.
Reports are verified and shared with the DEC to ensure timely updates. -
Reporting a Bloom
Think you’ve seen a HAB? Submit a report with photos to the NYS DEC or contact us.
Details here: https://www.dec.ny.gov/chemical/83310.html -
How to Spot a Bloom
Learn what to look for and how to distinguish HABs from harmless algae.
DEC HABs Photo Guide (PDF)
More Information about Cyanobacteria
Volunteers submit both “bloom” and “no bloom” reports into an online reporting system. Canandaigua and Keuka Lake Associations also use this system. Bloom reports are depicted on the map on this page for only Seneca Lake. Please visit Canandaigua Lake Watershed Association or Keuka Lake Association websites to learn about those watershed’s HAB’s season.
Research on HABs in Seneca Lake
Pure Waters provided funding for research on Seneca Lake related to HABs. Professor John Halfman, Hobart and William Smith Colleges, was the lead researcher. He also conducted similar research on Owasco Lake. Each year he compiled the data and published a report on his findings. The 2021 report is interesting as the HAB experience was quite different for each lake, yet most conditions were essentially the same. Results from this research can be found by following the links below
