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!



This has been an interesting week for water quality. As we reported earlier this week, on Tuesday, September 8th (the Day after Labor Day) the lake was experiencing a significant bloom event along much of the 36 miles of shoreline. Conditions ranged from areas with light streaking and heavy suspended algae, to full on pea-soup conditions. 22 bloom reports were filed by volunteers on 9/8 (see a sampling of photos below). By Wednesday - also a calm, sunny day- many shoreline areas were clear, though we did receive a few reports of mid-lake streaking. 3 bloom reports were filed on Wednesday the 9th. Many additional shoreline and mid-lake surveys were performed by the Watershed Manager as well.​

​The cooler temps and slight north wind on Thursday and today seem to have kept blooms at bay. We are seeing some foam accumulation today.​

Historically, September has been the month where we experience our most intense blooms in terms of CyanoChlorophyll values (blue green algae) and microcystin values (the toxin associated with blooms). In September 2018, several CyanoChlorophyll values skyrocketed into the 1,000s (ug/L), when the DEC threshold for a bloom is 25 ug/L. Many of these blooms also had high toxin values. In 2019, our highest values were also in the month of September. While we have not yet surpassed previous year’s levels, this is a good reminder that when blooms pop up, they need to be avoided because they have the ability to be potentially harmful to your health or the health of our pets.​

Here is a table of the samples collected this week. Values are reported in ug/L, which is micrograms per liter. DEC threshold for a bloom is 25 ug/L.

.As you can see, many of the Blue Green Algae levels were very high along the shoreline areas. The four open water samples were well below bloom threshold and were collected to get a sense of levels away from the shoreline. We did have a few reports of blooms in the open water which is why we tell people to use their visual indicators before recreating in the lake. In fact, on Wednesday we had the reverse happen where the Yacht Club shoreline was clear of any visible algae and there were documented blooms of algae out in the mid-lake area.

Several other area lakes have also seen an uptick in blooms overs the last week, including Cayuga, Skaneateles, Owasco, Keuka and Hemlock.​

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. Please continue to use your visual indicators to look for surface streaking, pea-soup like conditions, and green cloudy water. These areas should be avoided.​​

For more information throughout the week, you can check out the interactive Bloom Map from the volunteer efforts, which is updated in real-time on the CLWA website. Click on the dots to pull up more information on each bloom (date reported, images of blooms, description, etc).



Drinking Water

The six Canandaigua Lake water purveyors (the City of Canandaigua, the Village of Newark, the Village of Palmyra, the Village of Rushville, the Town of Gorham, and Bristol Harbour) are working alongside the Geneva District Office of the Health Department and the New York State Department of Health to monitor the public drinking water for the presence of toxins associated with harmful algae blooms. Samples of the public drinking water are routinely collected and sent to a State approved laboratory during the harmful algae bloom season to determine if toxins are present. Samples were collected the morning of September 8th and all treated finished water results were below the detection limit.

CLWA and the Watershed Council works with the water purveyors and the Geneva District Office of the Health Department to receive the results and make them available to the public. So far this year, all results from the finished drinking water have come back non detect. Results from routine sampling can be viewed here:

Private water system users that draw water from the lake (those who are using a home treatment system where water does not come from a public water treatment plant) may face challenges during active blooms due to the varying capabilities of household treatment units to remove cyanotoxins. We encourage those using a private system to use bottled water during active blooms and to work with a professional water service company to evaluate their treatment system.

After a “quiet” couple of weeks with minimal harmful algal bloom reports from staff, volunteers and the public, today’s calm, sunny and hot weather has encouraged a substantial increase in Harmful Algal Blooms (HABs) throughout much of Canandaigua Lake’s 36 miles of shoreline. We have completed visual inspections, collected samples and have received numerous reports from the north end all the way down to the Woodville area and on both sides of the lake. In most areas it is light streaking and heavy dots at the shoreline area, however we have several reports and pictures of pea soup concentrations of HABs, most notably in the northeast section of the lake. We are also getting reports of mid-lake streaking as well.

While the sunny, calm, warm weather forecasted for the next few days will be great for getting in those end-of-summer activities, it is also ideal conditions for blue green algae (cyanobacteria) to pop up. As we cannot predict when or where blooms may appear, please continue to use your visual indicators before recreating in the lake. Please use caution before letting your pets in the water as well (check out this Dogs and HABs brochure for more information). September has been the month when we have experienced our most significant bloom events. A few recent samples of moderate blooms had high levels of cyanotoxins- so it is critical to avoid areas that have HABs streaking at the surface to full, dense HABs.

The pictures below are examples of the blooms that we have seen today that need to be avoided. It is also critical to avoid areas that are green and cloudy as well.

Thanks to all that sent in reports today.

Kevin Olvany

Watershed Program Manager, Canandaigua Lake Watershed Council

Lindsay McMillan

Association Director, Canandaigua Lake Watershed Association

More Information on Blue Green Algae

Click below for our Harmful Algae Bloom brochure.

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205 Saltonstall Street Canandaigua, NY 14424 • 585.396.3630