Sunday September 20, 2026, Honeoye Lake Water Quality

Terry Gronwall

40 minutes ago

3 min read

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We reported a lake wide blue-green algae bloom to the DEC NYHABS site over the last week. This lake wide blue-green algae bloom occurred because the lake was absolutely calm on Thursday 9/17 allowing the blue-green algae to rise to the surface and lasted only 1-2 days except in near shore areas where the blue-green algae are still trapped in weed fragments. Conesus Lake also had a whole lake blue-green algae bloom on Thursday 9/17 due to calm winds.

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Sunday September 20, 2026, Honeoye Lake Water Quality

Surface Water Temperature: ~70.7 F

Water Clarity: ~7.3 Feet

Lake Level: 803.0 Feet above sea level

Lake level is a little below weir level. Evaporation will lower the lake level 0.1 to 0.4 inches per day from this level unless we get more rain soon.

Observations: Sunday (9/20/26), Water clarity was ~7.3 feet an increase of ~0.7 feet (~8.4 inches) since last week. Today’s water clarity was ~3.3 feet higher than it was on September 18, 2025. The surface water temperature was ~70.7 F about a 1.8 F decrease over the last week.

The lake is in a very typical September water quality pattern this year with surface water temperature rapidly dropping every week. This morning had an overcast sky with a light northwest wind.

There have been 25 Honeoye Lake blue-green blooms reported to the DEC NYHABS site since June 29. We reported a lake wide blue-green algae bloom to the DEC NYHABS site over the last week. This lake wide blue-green algae bloom occurred because the lake was absolutely calm on Thursday 9/17 allowing the blue-green algae to rise to the surface and lasted only 1-2 days except in near shore areas where the blue-green algae are still trapped in weed fragments. Conesus Lake also had a whole lake blue-green algae bloom on Thursday 9/17 due to calm winds. The 5 blue-green algae blooms reported to the DEC NYHABS site over the last 2 weeks are dark blue in color. See the Honeoye Lake DEC NYHABS Honeoye Lake map below:

We are now in the peak blue-green algae bloom time period across all of the Finger Lakes. The dark blue circles are booms reported in the last two weeks. See Finger Lakes DEC NYHABS map below:

Always use your own visual assessment before making contact with the lake water at this time of year as the blue-green algae situation can change daily if not hourly. Please regularly check the DEC HABs alert map for more detailed updates on Honeoye Lake HABs alerts:

https://experience.arcgis.com/experience/e5dec19912454731a308bbb7af605fb3/

Visually we found a slight decrease in amounts of Anabaena (Dolchospermum) (looks like a spring or chain of beads), Microcystis (looks like a group of small round cells), Limnoraphis (looks like a rod), and Aphanizomenon (looks like a leaf) again today. cells) today. We also found a lot of Ceratium (looks like a small spaceship) which is not a blue-green species today. See algae images on the left and below: You should be watchful for Anabaena, Microcystis, Limnoraphis, and Aphanizomenon blooms, all cyanobacteria species, lake wide over the next few weeks particularly when we have sunny 80-90 F days with calm winds. More information on Gloeotrichia and Anabaena which are cyanobacteria can be found at: https://www.honeoyelakewatershed.org/habs

Several research studies have found that most of the phosphorus that fuels Honeoye Lake’s blue-green algae blooms is released from the lake bottom sediments when the lake’s dissolved oxygen level goes below 0.5 mg/L in the deeper parts of the lake breaking the phosphors/iron bond in the bottom sediments releasing phosphorus into the water column. The dissolved oxygen (DO) level near the lake bottom at 9 m (30 feet) was 5.94 mg/L today. This means that additional phosphorus is not currently being released from the lake’s bottom sediments at this time. Today’s temperature and dissolved oxygen graphs are posted on the left.

Honeoye Lake completely mixed again about a week ago. The lake is still isothermal meaning the water temperature is uniform from the surface to the bottom. The dissolved oxygen is well mixed too. Ranging from 7.77 mg/L at the surface to 5.94 mg/L near the bottom. The blue-green algae in the lake should gradually dissipate now that the water temperature is getting colder every week.

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