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  • Terry Gronwall

August 27, 2020 Update - Lake Isothermal (Click Here)

Updated: Aug 28

We noticed today, Thursday August 27th, 2020 that the lake had about the same level of algae in the water column and water clarity level as last Monday. When we returned home, we found an Anabaena bloom that looked like pea soup and a water snake near our dock. Anabaena blooms have the potential to produce toxins that could affect people and their pets. See pictures below:


Because last Thursday’s mixing (turn over) event mixed nutrients released by the bottom sediments when the dissolved oxygen level was below 1 ug/L into the water column, we are likely to continue to have an Anabaena and Microcystis blooms for the next few weeks. An Anabaena bloom looks like pea-soup and an Microcystis bloom looks like green paint on the lake surface. Be extra watchful for new blue-green algae blooms for the rest of the summer. Please report any suspicious blooms to us at

watershedtaskforce@gmail.com and the NYSDEC “Know it, Avoid it, Report it” at https://survey123.arcgis.com/share/66337b887ccd465ab7645c0a9c1bc5c0


Today, Thursday August 27, 2020, the lake was isothermal due to all the cold rain we have gotten this week. Isothermal means the water column has uniform water temperature from top to bottom. The dissolved oxygen level was also relatively high and uniform from top to bottom in the water column. This means that currently no additional legacy phosphorus is being released from the bottom sediments given the relatively high dissolved oxygen level near the bottom.


1 meter (m) = 3.3 Feet and 1 Degree Centigrade ( C ) = 1.8 Fahrenheit (F)

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://nysdec.maps.arcgis.com/apps/webappviewer/index.html?id=ae91142c812a4ab997ba739ed9723e6e


August 24, 2020 Honeoye Lake Update (Click Here)


Surface Water Temperature: 77.7 F

Water Clarity: 4.3 Feet

Lake Level: 803.1 Feet above sea level

Lake Level Relative to Weir: -0.4 Feet

Observations: Monday (8/24/20), lake is experiencing a lake wide blue-green algae bloom due to the nutrients that were mixed in the water column last Thursday when the lake had its traditional late August lake mixing (turn over) event. There was medium to heavy Anabaena (blue-green algae) visible in the water column at most of our 10 near shore and open water HABs monitoring locations. We did see light to heavy surface algae scum in some areas. Pictures that we took today at our open water lake sampling site and near the North Shore are shown below:



Anabaena is a species of blue-green algae that we see starting in July and August usually after a lake mixing (turn over) event. Anabaena has the potential to produce toxins that can be harmful to people and pets. We strongly urge you to follow the DEC guidelines of “Know it, Avoid it, Report it” For more info go to: https://www.honeoyelakewatershed.org/habs

Water clarity has decreased by ~1.2 feet to 4.3 feet since last week due to an increase in algae in the water column. This is lower than normal water clarity for late August (Water Clarity Ave. ~6.6 Feet). Surface water temperature declined about 0.7 F to 77.7 F.


Last Thursday August 20, 2020 the lake completely mixed (turned over) because of the relatively low air temperature of ~50 F last Wednesday night. You can see that on our temperature and dissolved oxygen charts to the left. Last Thursday 8/20 the surface water temperature was 24.9 C and the bottom temperature was 24.6 C. Temperature difference of only 0.3 C. The dissolved oxygen level at the surface was almost the same as at 9 m. This condition is called isothermal and confirms a complete lake mixing (turn over) event.

1 meter (m) = 3.3 Feet and 1 Degree Centigrade ( C ) = 1.8 Fahrenheit (F)


Today (Monday 8/24) we found the lake starting to re-stratify to start this legacy nutrient sediment releasing cycle from bottom sediments all over again once the bottom water becomes anoxic. We will keep you posted as this develops.


Now that the lake has mixed (turned over), we are likely to have Anabaena and Microcystis blooms for the next several weeks. An Anabaena bloom looks like pea-soup and a Microcystis bloom looks like green paint on the lake surface. Be extra watchful for new blue-green algae blooms for the rest of the summer. Please report any suspicious blooms to us at

watershedtaskforce@gmail.com and the NYSDEC at https://survey123.arcgis.com/share/66337b887ccd465ab7645c0a9c1bc5c0

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://nysdec.maps.arcgis.com/apps/webappviewer/index.html?id=ae91142c812a4ab997ba739ed9723e6e

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Honeoye Lake Watershed Task Force Members:

Town of Richmond

Town of Canadice

Town of Bristol

Town of South Bristol

Town of Naples

Honeoye Valley Association