Canandaigua Lake Drinking Water & Algal Blooms: What to Know

Last reviewed: October 9, 2026. General information only, not medical or engineering advice. Follow current advisories from your water supplier, the Ontario County or Yates County health department, and the NYS Department of Health.

Canandaigua Lake is a working drinking water reservoir as well as a place to swim and boat. Several public water systems draw from it, a state regulation protects it, and in late summer harmful algal blooms can appear along its shores. If you live near the lake, where your tap water comes from matters, and so does what you do on your property.

Who drinks Canandaigua Lake water

The Ontario County Soil & Water Conservation District describes the lake as a drinking water source for more than 70,000 people. The Canandaigua Lake Watershed Association lists six public water purveyors that draw from the lake: the City of Canandaigua, the Village of Newark, the Village of Palmyra, the Village of Rushville, the Town of Gorham, and Bristol Harbour. Five of them (all but Bristol Harbour) make up the Canandaigua Lake Watershed Commission, which enforces the lake’s watershed rules.

The City of Canandaigua says all water provided to city residents comes from Canandaigua Lake. Its FAQ notes the water is moderately hard (about 130 mg/L, or 7.6 grains), fluoridated at about 0.7 parts per million, and disinfected with chlorine from sodium hypochlorite rather than chloramines.

The state rules that protect the lake

A section of the state sanitary code, 10 NYCRR §132.1, applies specifically to Canandaigua Lake and its tributaries. Beyond the septic provisions covered in our septic guide, it includes rules most residents never hear about:

No bathing, boating, fishing from boats or through the ice, or trespassing within 300 feet of the public water supply intakes.
No animals or poultry may stand, wade, swim, or be watered in the lake within 300 feet of a public water intake.
No garbage, refuse, or other polluting matter may be deposited in the lake or a watercourse, or within 100 feet of them in Zone I where it could wash in.
Boats may not discharge excreta, garbage, or other waste into the lake. Boats with toilets or galleys must use removable watertight receptacles.
No manure pile within 100 feet of the lake or a watercourse in Zone I.

State Navigation Law §33-a also makes it unlawful to operate or moor a boat on Canandaigua Lake (along with Lake George, Keuka, Skaneateles, and Greenwood Lakes) with toilets, sinks, showers, or similar equipment that drain into the lake. They must be removed, sealed, or drain to a tank that can be pumped or carried ashore.

Harmful algal blooms and public water

Cyanobacteria (blue-green algae) blooms have become a seasonal concern on Canandaigua Lake. According to CLWA, the six public water purveyors work with the State Health Department’s Geneva District Office and the NYS Department of Health to sample public drinking water for algal toxins during bloom season, with results posted publicly. CLWA notes that conventional treatment (coagulation, sedimentation, filtration, and chlorination) can generally remove intact cyanobacteria cells and low levels of toxins, but that severe blooms can challenge water systems.

The City of Canandaigua says that during HAB season, which it describes as August to October, its plant tests raw and finished water for microcystin, and that microcystin has never been detected in the plant’s finished water.

If toxins ever exceed health advisory levels in a public system, the NYS Department of Health and the water system notify the public about using alternative water for drinking, infant formula, ice, brushing teeth, and food preparation. CLWA’s page lists the U.S. EPA’s 2015 ten-day health advisory levels: for microcystins, 0.3 µg/L for children under six and 1.6 µg/L for school-age children and adults; for cylindrospermopsin, 0.7 and 3.0 µg/L respectively.

If you draw water straight from the lake

Some lakeside homes use a private intake with a home treatment system. This is where the risk is concentrated. CLWA’s guidance is blunt: never drink untreated surface water, and when blooms are present, don’t drink water drawn directly from the lake even if it’s treated by in-home units, and don’t use it for infant formula, ice, brushing teeth, preparing food, or washing dishes. Boiling, UV, and ordinary filtration don’t remove the toxins. Some treatment units have been shown to reduce microcystin, but CLWA says it isn’t known whether they bring it to a safe level, and private supplies aren’t regulated or monitored.

The NYS Department of Health adds that people using surface water should connect to public water if they can, or consider a private well drilled by a DEC-registered well driller.

Questions to ask before buying a house on a lake intake

Is public water available at the road? Which purveyor, and what does connection involve?
What treatment is installed, who services it, and are there records?
Is there space for a drilled well that meets septic separation distances?
What did the previous owners do for drinking water during bloom season?
How is the intake line protected in winter?

If you’re buying near the lake

Water questions belong on the same list as the septic and dock questions:

Confirm the water source in writing: public main, private well, or lake intake.
For public water, read the supplier’s most recent annual water quality report and note who to call with questions.
For a well, ask for recent test results from a laboratory certified by the NYS DOH Environmental Laboratory Approval Program, and test again as part of your purchase.
For a lake intake, budget for a different drinking water source during bloom season at minimum, and ask the water district about connecting.
Check the 300-foot zones if the property is near a public water supply intake; swimming and boating are restricted there under 10 NYCRR §132.1.

Recognizing and reporting blooms

Blooms can look like spilled paint, pea soup, or floating scum, in green, blue-green, or other colors. It’s hard to tell a toxic bloom from a harmless one by eye, so the advice from CLWA and the Health Department is to avoid discolored water or scum, keep pets and children out, and rinse off with clean water after any contact. Dogs are at particular risk because they drink lake water and lick their fur.

CLWA and the Watershed Council run a shoreline HAB monitoring program with DEC and the Finger Lakes Institute. To report a suspected bloom on Canandaigua Lake, CLWA asks you to email a photo with the location to HABs@canandaigualakeassoc.org. You can also report to DEC at HABsInfo@dec.ny.gov. Report symptoms in people to the Ontario County Health Department.

Who to contact

City of Canandaigua water plant: 585-396-5064 (per the city’s FAQ) for city water questions.
Your water purveyor if you’re served by Gorham, Newark, Palmyra, Rushville, or Bristol Harbour: check your bill or annual water report for contact information.
Canandaigua Lake Watershed Association: 585-394-5030, for bloom reporting and water quality updates.
Ontario County SWCD / Watershed Inspector: 585-396-1450, for septic and watershed rule questions.
Canandaigua Lake Watershed Council: 585-233-3630, for watershed programs and local law information.
Ontario or Yates County Health Department: for private well questions and to report bloom-related illness.

Swimming, pets, and kids during bloom season

Most days, most of the lake is fine for swimming. The practical rule from the Health Department and CLWA is simple: if the water is discolored, looks like paint or pea soup, or has scum, stay out and keep pets out. Rinse off with clean water after swimming, especially before letting a dog lick its coat. Watch for symptoms such as vomiting, diarrhea, rash, or eye and throat irritation after contact, and call a doctor or vet if they appear. If you rent your house to guests, put a short note about blooms in the house guide.

Blooms can appear in different places at different times of day, so a clear morning doesn’t guarantee a clear afternoon. Check the shoreline each time before swimming, and teach kids what a bloom looks like. CLWA’s email updates during bloom season are the easiest way to hear about conditions around the lake.

What lakeside owners can do

Keep your septic system inspected and pumped; see our septic guide.
Skip phosphorus fertilizer and keep a vegetated buffer along the shore.
Manage roof and driveway runoff so it soaks in rather than running to the lake.
Keep pet waste, yard waste, and chemicals away from the shoreline and ditches.
Use pump-out facilities for boat holding tanks.

Seasonal checklist

Spring: test any private well, service treatment equipment, and check intake lines after winter.
Late summer to fall: sign up for CLWA water quality updates, watch the shoreline, and have bottled water on hand if you use lake water.
Fall: winterize seasonal intakes and plumbing following the installer’s instructions.

Official sources

Related: Septic inspections · Dock rules

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