Sunday September 28, 2025 Honeoye Lake Water Quality

Terry Gronwall
Sep 28
3 min read

Very little change in the lake wide blue-green algae bloom over the last week. The lake is anoxic between 7.5-9 m (24.8-30 Feet) again. Muller Field Station September 2025 newsletter.

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Surface Water Temperature: ~69.3 F

Water Clarity: ~4.6 Feet

Lake Level: 802.6 Feet above sea level

Observations: Sunday (9/28/25), Water clarity was ~4.6 feet about the same as last week. The surface water temperature was ~69.3 F about 0.9 F warmer than last week. A beautiful day to be out on Honeoye Lake as fall color is starting to appear!

There has been very little change in the amount of blue-green algae in the water column over the last week. Therefore, we expect that there will continue to be surface blue-green algae blooms at isolated near shore and open water locations around the lake given the amount of blue-green algae in the water column for the next few weeks particularly when we have 80-90 F days with calm winds. There were 6. blue-green algae blooms on Honeoye Lake reported to the NYS DEC HABs alert map, dark blue circle, over the last two weeks. The light blue circles are blue-green algae blooms reported to the DEC more than two weeks ago. See NYS DEC HABs alert map below: Since Honeoye Lake has ~10 miles of shoreline your most accurate source of blue-green algae blooms is the crowd source bloom data found on the DEC HABs alert map (NYHABS).

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

The Finger Lake Region has been experiencing heavy HABs over the last few weeks. September is often the peak month for HABs. See today’s DEC Finger Lakes HABs alert map below:

Anabaena (Dolchospermum) (looks like a spring or chain of beads), Limnoraphis (looks like a rod), and Microsystis (looks like a group of small round cells) are the current dominant blue-green algae species. See picture on the left. You should be watchful for Microcystis, Anabaena, and Limnoraphis blooms lake wide. These are all blue-green (cyanobacteria) algae species. More information on blue-green algae 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 anoxic (dissolved oxygen 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 7.5-9 m (24.8-30 feet) was 0.48-0.38 mg/L today. This means that phosphorus is currently being released from the deep bottom sediments into the deepest part of the lake water. We had a complete lake mixing event in late August that mixed the deep lake water, with excessive amounts of phosphorus, with the whole water column fueling the blue-green algae bloom the lake has been experiencing in September. See temperature and DO graphs to the left.

You can see the complete lake mixing event in late August on the above Temperature and Dissolved Oxygen graphs where the 0-9 m lines have converged to the same level. Also, you can see that today the lake has become anoxic between 7.5-9 m again on the dissolved oxygen graph. If the lake mixes in the next week or so this should have minimal effect. If it continues for a few weeks, we will get another increase in phosphors fueling more blue-green algae blooms when the lake does mix again.

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/

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