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Water quality update for September 18, 2020

Cooler daily temps and chilly nights certainly have us feeling like the end of summer is near! The cooler temps have also resulted in fewer reported blooms. However, we know they can still pop up when the conditions are just right. In fact, this week volunteers reported 3 potential blooms out of the 27 shoreline surveys that were performed.

On Thursday, we received results from the microcystin toxin analysis that was performed on samples collected from both intense bloom areas and open water non-bloom areas the day after Labor Day (Tuesday, September 8th). While these results are 10 days old and not indicative of current lake conditions, they are of interest because 9/8/2020 was our most significant day of blooms this summer, with many areas of the lake experiencing streaking and/or green colored water. It further confirms that blooms need to be taken seriously.

How to interpret these results:

  • The values in this table are reported in ug/L, which is micrograms per liter.

  • DEC threshold for a bloom is 25 ug/L of CyanoChlorophyll (blue green algae).

  • Microcystin is the toxin that may be produced during a bloom. Microcystin advisory thresholds for shoreline and open water can be found in the graphic below.

  • Microcystin results came from a NY State certified lab.​​​​​


When reviewing these results, you will note that the four samples from open water areas (samples collected from a boat) were all well under the DEC threshold for a bloom. Shoreline areas on the other hand, all had extremely high CyanoChlorophyll levels, well over bloom threshold.

The story is the same for toxin results. Open water samples had less than 1 ug/L of microcystin. All the shoreline samples that were sent on for toxin analysis came back well above the 20 ug/L NYS threshold for a “High Toxin” bloom.


These results are showing us that shoreline – as well as open water areas – in active bloom situations must be avoided, as they have potential to have extremely high toxins that can be harmful to humans and pets. The shoreline areas with shallower, warmer waters have the highest likelihood of a potentially harmful bloom, and it is often where water recreation occurs.

Conditions have changed greatly since the day these samples were collected, and remarkably, the day after these samples were collected the water appeared very clear in many areas.

As summer draws to a close next week, we hope to still get in a few more nice lake days! Please remain aware that conditions can change quickly and to keep an eye out for signs of a bloom before you or your pets enter the water - look for surface streaking, pea-soup like conditions, and green cloudy water. These areas should be avoided.

In coming weeks, we hope to share more info on projects and programs in action that are aimed at protecting Canandaigua Lake water quality. We know that a healthy, protected watershed is one of the keys to clean water. Please considering tuning into a webinar next Wednesday, September 23rd at 10:00 on the gypsy moth, which has been devastating out watershed forests this year. The program is hosted by Finger Lakes ReLeaf, and registration is required. We hope you’ll tune in to learn more!



More Information on Blue Green Algae

Click below for our Harmful Algae Bloom brochure.

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