Seneca Lake algae bloom status

Seneca Lake algae bloom history

New York's Department of Environmental Conservation listed Seneca Lake as having a harmful algal bloom every year from 2015 to 2025.

In 16 years, a bloom here was confirmed with high toxin levels, the most serious category the state recorded (tracked from 2012 to 2018).

Blooms were confirmed by state staff in 11 years; in the other years they were reported as suspicious but not confirmed.

Blooms have been recorded every year for the last 11 years in the data.

That puts Seneca Lake in the top 10% of the 352 New York lakes on this site for the number of years with blooms.

When do algae blooms happen at Seneca Lake?

At Seneca Lake, reports are most often logged in July, August and September.

About 100% of reports fall between May and September, when warm, calm, sunny weather lets blue-green algae multiply.

Blooms can appear, move with the wind and fade within hours or days, so the time of year is only a guide.

Recent Seneca Lake algae reports

New York publishes one entry per lake for each season it appears on the bloom list, showing when it was first and last listed and its highest status.

What the New York results mean

New York sorts each bloom by how far it has been checked.

Suspicious bloom

Reported to the state but not yet confirmed as blue-green algae.

Confirmed bloom

State staff confirmed blue-green algae from photos or a sample. Avoid contact where the bloom is.

High toxins

Toxin levels high enough to be a health concern. Recorded separately from 2012 to 2018.

Is Seneca Lake safe for dogs?

Dogs are at the greatest risk from toxic algae. They swallow water while swimming, eat scum on the shore and lick algae off their fur afterwards, and a small amount can kill a dog within hours. With blooms recorded in 11 different years here, take particular care at Seneca Lake in July, August and September.

• Keep your dog on a lead near water that looks green, scummy, foamy or discoloured, and away from algae washed up on the shore.
• If your dog gets in, rinse it straight away with clean water and don't let it lick its coat.
• Call a vet immediately if your dog vomits, drools, has diarrhoea, staggers, shakes or seems weak after being near the water.

Read the full guide to toxic algae and dogs: symptoms, what to do in the first minutes and how vets treat it.

Health effects of toxic algae

Blue-green algae (cyanobacteria) can produce toxins that affect the liver, nervous system and skin. Swallowing water during a bloom can cause stomach pain, vomiting and diarrhoea. Skin contact can cause rashes, and breathing spray from the water can irritate the eyes, nose and throat. Children are at higher risk because they are smaller and more likely to swallow water.

How to spot a bloom

Toxic blooms can look like pea soup, spilled paint or green streaks on the surface, and they can also be blue, brown, white or red. Scum often collects along the shore downwind. If you can't see your feet in knee-deep water, or you aren't sure, stay out.

Don't drink untreated lake water, and don't boil it to make it safe: boiling doesn't destroy algal toxins. If you feel unwell after contact with the water, contact a doctor or Poison Control on 1-800-222-1222.

Nearby lakes with algae reports

• Cayuta Lake15 km away, 12 reports, last in 2025
• Lamoka Lake16 km away, 7 reports, last in 2025
• Lamoka Lake Channel17 km away, 3 reports, last in 2023
• Waneta Lake18 km away, 16 reports, last in 2025
• Keuka Lake22 km away, 10 reports, last in 2025

All Seneca County lakes with algae reports

Questions about Seneca Lake

Is there algae in Seneca Lake right now?

Seneca Lake was on New York's harmful algal bloom list from 22 July 2025 to 28 October 2025, with confirmed bloom status (158 reports). New York publishes its data once a year, so for today's conditions check the NYHABS map and the signs at the shore.

When was the last algae bloom at Seneca Lake?

The most recent entry in New York's data is from 22 July 2025: a confirmed bloom.

Has Seneca Lake had toxic algae before?

Yes. Blooms are recorded every year from 2015 to 2025, most often in July, August and September.

Can dogs swim in Seneca Lake?

Keep dogs out of the water whenever a bloom is reported or the water looks green, scummy or discoloured. Dogs are the animals most often killed by algal toxins because they swallow water and lick their fur. If your dog swims in water that might have algae, rinse it with clean water and call a vet if it vomits, drools, staggers or seems weak.

Can you eat fish caught in Seneca Lake during a bloom?

If you keep fish caught during a bloom, health agencies advise removing the guts and liver and rinsing the fillets in clean water before cooking, because toxins collect most in the organs. Some agencies advise not eating fish from an active bloom at all, so follow local guidance.