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  • Terry Gronwall

Thursday August 19th, 2021 Honeoye Lake Water Quality Update

Wednesday 8/18 afternoon and evening through Thursday 8/19 morning we got 3+ inches of rain at Honeoye Lake. This rain event and the wind associated it with caused a lake mixing event down to 26-27 feet of water depth in the lake.

This mixing of nutrients released from the bottom sediments with the surface water in the lake caused a a significant increase in blue-green algae decreasing the water clarity from 7.9 feet last Monday to 4.3 feet today.

To the left you can see the Anabaena and Microcystis bloom that occurred near our dock starting today (Thursday 8/19).

Microscope of images are shown below:

Anabaena Microcytis

You can see the lake mixing event on the today's temperature and dissolved oxygen charts to the left. You can compare this chart with the chart from last Monday below to see the mixing event more clearly: Also, last Monday's report contained an explanation of what the impact of the next lake mixing event would be.

This potentially creates the conditions for blue-green algae blooms over the next several weeks.

The DEC recommends that you, your family, and pets avoid contact with water that contains blue-green algae bloom like Anabaena and Microcystis. Everyone should be very careful to watch for blue-green algae blooms for the next few weeks.


Monday August 16th, 2021 Honeoye Lake Water Quality Update

Surface Water Temperature: 77.0 F

Water Clarity: 7.9 Feet

Lake Level: 803.4 Feet above sea level

Lake Level Relative to Weir: -0.1 Feet

Observations: Monday (8/16/21), The water clarity has increased ~0.65 feet over the last week to 7.9 feet and the surface water temperature has remained the same as last Monday (8/9/21) at 77.0 Fahrenheit. There was light Anabaena and Microcystis visible in the water column in most areas of the lake this morning. We did not see any blue-green algae surface scum. Again, it was another beautiful day to be out enjoying Honeoye Lake!

We took the image of today’s Anabaena and Microcytes algae samples below using a high-powered microscope. We also found Ceratium which is considered a harmless aquatic organism. For more information on Anabaena and Microcystis see the articles at HARMFUL ALGAL BLOOMS | Honeoye Lake (


Anabaena and Microcystis

We also continued to notice a lot of filamentous green algae trapped in shallow water areas where the aquatic vegetation is growing to the lake’s surface. This green filamentous algae is mostly an aesthetic and recreational lake issue. However, there is probably some blue-green algae trapped in with it too. So, you should avoid contact with it. If it is in 5 feet or deeper water you can request that our weed harvester remove as much of it as possible by e-mailing:

The DEC recommends that you, your family, and pets avoid contact with water that contains blue-green algae bloom like Anabaena and Microcystis. Everyone should be very careful to watch for blue-green algae blooms for the next few weeks.

The lake mixed down to 8 m on Thursday July 29th. When the lake mixed, it mixed some bottom water with phosphorus and ammonia released from the bottom sediments into the whole water column. This is what fueled our Anabaena and Microcystis bloom starting the first week of August. The lake has now restratified again which will cause legacy phosphorus to be released from a significant area of the bottom sediments all over again.

When a lake stratifies and forms a thermocline the decaying organic matter, dead algae and weed fragments, on the lake bottom consumes dissolved oxygen (DO) in the water below the thermocline. When the DO has been completely consumed the phosphorus iron bond in the bottom sediments becomes weak releasing legacy phosphorus into the water near the bottom sediments. Surface water temperature 77.0 F. Bottom water temperature 72.1 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:

The first week of August we made aquatic vegetation maps for use by the Honeoye Lake Weed Harvesting crew to give them information to be able to focus their efforts on areas of the lake where aquatic vegetation is growing to the lake surface (red areas on the maps). See our early August 2021 maps below:

We found that the aquatic vegetation growth has significantly increased from early July as shown by the increase in red areas on our aquatic vegetation maps indicating vegetation growing to near the water's surface potentially impeding recreational us of the lake. See 2021, 2020, & 2019, August macrophyte maps at AQUATIC VEGETATION MANAGEMENT | Honeoye Lake (

Click on the blue outlined box that says "Log in / Sign up" in the upper right hand corner of this page to sign-up to be notified when we update our weekly Honeoye Lake water quality blog.


- Click on this link to see the new HLWTF Honeoye Lake Watershed Storm Water Took Kit if you are planning any storm water projects on your property:

- Click on this link for "2021 Honeoye Lake Aeration Engineering Planning Project"

- Click on this link for HLWTF Winter newsletter: e6fc30_ef8d01223f42408ba11b3a7a5f83bebe.pdf

- Click on this link for "2020 Water Quality: What, Why, What's Next"

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