Harmful Algal Bloom Season on Keuka Lake: A Household Plan

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Last reviewed: October 9, 2026. General information only, not medical or veterinary advice. Follow current guidance from the NYS Department of Health, NYSDEC, and your local health department. If a person or pet shows symptoms after contact with a bloom, seek medical or veterinary care right away.

Harmful algal blooms (HABs) have become part of late-summer life on many Finger Lakes, and Keuka is no exception. In August 2026, Finger Lakes 1 reported that the state’s HAB data showed 12 confirmed reports on Keuka Lake since July 24, reported by the Keuka Lake Association and the public. Blooms can appear in one cove and not the next, and can come and go within hours.

You can’t control when a bloom shows up off your dock. You can have a plan. This guide is a household HAB plan for Keuka owners: how to recognize a bloom, where to check, rules for swimming, pets, drinking water, and boating, what to do after contact, and how to report. If your home draws water from the lake, also read our drinking water and lake intake guide.

What a HAB is

NYSDEC’s HABs page explains that freshwater HABs are usually visible patches of cyanobacteria (blue-green algae). Cyanobacteria are naturally present in most lakes in low numbers, but under certain conditions they multiply rapidly. DEC says blooms are likely triggered by a combination of factors: excess nutrients (phosphorus and nitrogen), lots of sunlight, low water or low flow, calm water, and warm temperatures. Some types produce toxins that can harm people and animals through swallowing, skin contact, or breathing in spray.

DEC also notes that blooms can be short-lived (appearing and disappearing in hours) or long-lived (lasting weeks).

How to recognize a possible bloom

DEC’s photo guide says HABs may look like:

  • parallel streaks, usually green, on the surface
  • green dots, clumps, or globs
  • spilled paint: blue, green, or white
  • water that’s bright green or like pea soup

Not every algae is harmful. DEC shows non-toxic green algae that can look like floating rafts, bubbling scum, silky or hairy growth on rocks, or stringy mats. Because it’s hard to tell the difference by eye, DEC’s advice is simple: when in doubt, stay out. People, pets, and livestock should avoid contact with floating mats, scums, or discolored water, including shades of green, blue-green, yellow, brown, or red.

Your household HAB plan

1. Know it: check before you go in

  • Look at the water at your dock or beach before anyone swims, every time, during bloom season. Conditions change quickly.
  • Check DEC’s HAB notifications page. DEC cautions that if a waterbody isn’t listed, that doesn’t mean it has no bloom; it may not have been reported.
  • Follow local monitoring. The Keuka Lake Association runs a shoreline monitoring program and posts updates.
  • Sign up for DEC’s weekly HAB notifications through its email list (linked from the HABs page).

2. Avoid it: household rules

Write these down and share them with family, guests, and renters:

  • No swimming, wading, or water play in water that looks discolored or has scums or mats. DEC says the risk while swimming is greater when blooms cover a large part of a lake or are found in open water.
  • Keep kids and pets out of the water and away from beach debris and washed-up algae when a bloom may be present.
  • Don’t handle algae.
  • Steer boats and paddlecraft around visible blooms, and avoid churning through them.
  • Regulated swimming beaches are monitored, and DEC says swimming at them greatly reduces your exposure risk. Beach closures are made by health officials and beach operators.

3. Drinking water rules (lake-intake homes)

DEC and the Department of Health give the same core advice for people who use lake water at home:

  • Never drink, prepare food, cook, or make ice with untreated surface water, bloom or no bloom. Untreated surface water can also carry bacteria, parasites, and viruses.
  • During a bloom, don’t drink lake water even if it’s treated. DEC says in-home treatment such as boiling, chlorine, UV, and filtration units doesn’t protect against HAB toxins. Boiling doesn’t remove toxins.
  • Keep bottled water on hand all bloom season for drinking, cooking, ice, brushing teeth, and pets.

The Department of Health’s blue-green algae page has more detail, including guidance on other household uses during a bloom.

4. Pets

Dogs face the greatest risk because they swim through blooms, drink the water, and lick their fur afterward. DEC explains that HAB cells can stick to fur and become concentrated when an animal grooms itself, and that some blooms release a fast-acting nerve toxin that is dangerous to dogs.

DEC lists dog symptoms including:

  • stumbling, seizures, convulsions, or paralysis
  • excessive drooling
  • disorientation, inactivity, or depression
  • elevated heart rate and difficulty breathing

If you see these symptoms, especially within 30 minutes to a few hours of contact with a bloom, DEC says to get immediate veterinary care. If your pet has been in suspect water, rinse it with clean water. Tell the vet how long the exposure lasted. New York Sea Grant publishes a dogs and HABs brochure (PDF).

5. Fishing

DEC says it’s still being studied whether HAB toxins build up in fish, and there have been no reports of people becoming sick from eating fish caught during a HAB. As a precaution, New York advises anglers to avoid eating fish caught from areas with the thick paint-like or pea-soup coloring of HABs.

If someone has contact with a bloom

DEC’s guidance:

  1. Rinse thoroughly with clean water to remove algae.
  2. Watch for symptoms, including vomiting, nausea, diarrhea, skin, eye, or throat irritation, allergic reactions, or breathing difficulties.
  3. If symptoms appear after drinking or having contact with a bloom or untreated surface water, stop using the water and get medical attention.
  4. Tell your doctor and your local health department about the exposure. DEC notes that people vary in their sensitivity, much like with poison ivy.

Report it

If you see a suspected bloom, DEC asks you to submit its Suspicious Algal Bloom Report Form (linked from the HABs page), with close-up and wide photos showing location and extent if possible. If you can’t complete the form, email DEC at HABsInfo@dec.ny.gov. Report health symptoms to the Department of Health and your local health department. Reports help neighbors and contribute to the state’s data on Keuka.

What owners can do to reduce blooms

DEC identifies excess nutrients as one of the triggers. Lakeside owners can help limit what washes into the lake:

  • Maintain your septic system and have it pumped and inspected on schedule. See our septic guide.
  • Limit fertilizer near the shoreline, and keep grass clippings and leaves out of the water.
  • Keep vegetation along the shore and slow down runoff from roofs, driveways, and steep lawns.
  • Control erosion during construction projects. See our shoreline rules guide.

Printable HAB plan checklist

  • Bottled water stocked for drinking, cooking, ice, and pets
  • Household rule: look before anyone goes in
  • DEC notifications page and KLA updates bookmarked
  • Signed up for DEC HAB email notifications
  • Dog kept out of suspect water; clean rinse water ready
  • Local vet’s phone number posted
  • Guests and renters given the household rules
  • DEC report form bookmarked for suspected blooms

Frequently asked questions

When is HAB season on Keuka Lake?

DEC links blooms to warm temperatures, sunlight, calm water, and nutrients, which makes summer and early fall the usual concern. In 2026, Finger Lakes 1 reported confirmed Keuka blooms beginning in late July. Watch the water whenever it’s warm and calm.

Is it safe to swim if I don’t see a bloom?

Blooms can appear and disappear quickly, and one area can be affected while another isn’t. Look at the water before you swim, check DEC and KLA updates, and stay out of anything discolored or scummy.

Does boiling or filtering lake water make it safe during a bloom?

No. DEC says in-home treatment, including boiling, chlorine, UV, and filters, doesn’t protect against HAB toxins. Use bottled or another safe water source.

My dog swam in a bloom. What should I do?

Rinse your dog with clean water right away and watch closely. If you see stumbling, drooling, seizures, disorientation, or breathing trouble, especially within 30 minutes to a few hours, get to a vet immediately.

Who closes beaches during a bloom?

DEC says state parks, county officials, or the local health department can close swimming beaches, and beach operators close them as needed. DEC can’t close a lake.

Official sources

Related on Living on Keuka: Drinking water and lake intakes · Well water · Septic systems · Shoreline rules · Year-round living

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