This weekend marks the official end of the Volunteer Shoreline Harmful Algae Bloom Monitoring Program. We’d like to thank the 42 of volunteers for participating in the 10-week program this season! With the routine monitoring program winding down, we will take a few weeks to review the data and compile a season report to share with our members and the watershed community. Thank you for following our Friday updates and providing feedback – we hope they are useful to help you better understand the lake conditions and the activities that are occurring to monitoring the lake.

While our weekly Friday updates are concluding with the program’s end, we are still very tied in with monitoring the lake's condition through the secchi disk program and other professional monitoring efforts. We will be providing a few more updates this fall (with less frequency) to share relevant water quality information.

With very few suspicious blooms reported this week, we thought this would be a good time to shift to a discussion of our lake level.


We have been getting several calls about low lake levels for this time of year and for good reason! The lake level is about 8 inches below the guide curve for this time of year and about 5 inches below where it was at this time last year (see chart below). That may not seem like a lot, but if you can’t get your boat out of the boat slip or you have hit the lake bottom with your propeller- you definitely know that the lake is lower than normal.

The key question is: why is it lower? There are “mother nature” influences that really dominate the lake level system and there are also interconnected human influenced factors that can have some impact as well. The City of Canandaigua is charged with operating the outlet gates for the lake at the north end. There are two separate gate systems: the main outlet (behind Wegmans) and the feeder canal (next Seager’s and the Sailboard shop). The main outlet gates are behind Wegmans and those are a set of large gates that are opened to try and release a large volume of water to provide for flood control. The feeder canal gate is open all of the time and is managed to release 35 cfs (cubic feet per second) or about 22 million gallons a day to provide for enough stream flow for the Canandaigua Wastewater Treatment Plant and other wastewater plants on the outlet to discharge into without creating any environmental contamination issues. This is required by state law and is out of our local control.

22 million gallons a day seems like a lot - but it is important to remember that there is about 300 million gallons in the top inch of lake water. That is equivalent to 1 inch in lake level every 14 days. Summertime evaporation plays a much larger role. On a typical hot and sunny summer day we can lose approximately 50-60 million gallons per day through evaporation. That is equivalent to a 1-inch drop in the lake every 5-6 days! Our water supply has a minor impact on the lake with 10-15 million gallons a day being used as a water supply for about 70,000 people. Therefore, we lose the equivalent of about 1.0-1.5 inches of lake level every month.

With all of these outflows - how do we fill the lake back up? Precipitation on both the lake and the surrounding watershed provides the inflows to more than balance the lake level during most years. One way to prove that we have significant inflows is that on an average year, the main outlet gates are open about 100 days a year to release the excess water that enters the system to try and prevent flooding. However, this system is also limited at times if we get too much rain. When these gates are open, we can release about 200-500 million gallons a day (depending on lake level) that is equivalent to about 0.65 to 1.5 inches of lake level per day. In 2020, the main outlet gates have been closed since May 16th due to the dry conditions.

2020 has been a dry year - especially since mid-May. We have had a little over 10 inches of rain from late May to late September that fell on the lake and the surrounding watershed. We typically get another few inches of rain during this time frame. The rain on the lake alone does not supply enough water to sustain lake levels. The key to filling the lake is that the drainage area to the lake is about 10 times the size of the lake surface and has over 350 miles of streams that drain this system into the lake! However, since about early June the small to mid-size streams have been largely dry and the bigger streams like Naples Creek and West River- have had very low flows. This September was also one of the driest on record. All of these items in combination has provided the lake level deficit that we are now in.

On the hopeful side - Happy New Water Year! October 1st is the new hydrologic year- which is typically when the ground and stream systems are at their lowest level. We will start the see evaporation slow down and the rains will generate more runoff in the fall and winter seasons to fill the lake back up.

The first week of fall is upon us. We are starting to see docks coming out for the season, boats getting winterized, and a renewed focus on yard chores.

Here at CLWA, we are still going strong with a dedicated group of volunteers continuing to submit their weekly secchi disk reports and send in shoreline HABs surveys. We thank them for their ongoing efforts to provide us with lake condition reports. Last week (week ending 9/20), 9 volunteers submitted clarity readings with a weekly average of 5.47 meters, which was an increase in water clarity from the previous week’s average of 5 meters (week ending 9/13). Remember that clarity is a measure of algal abundance and suspended sediments in the water column. Volunteers also reported a drop in the average surface water temperature this past week. Clarity is increasing, and surface water temperatures are starting to decrease, which should result in fewer HAB reports as we move through October. 

We have, however, had several blooms reported so far this week, including three bloom reports coming in just this afternoon. Today's calm winds and sunny weather are the perfect conditions for HABs. Therefore, it is still wise to scan the shoreline before entering the water or letting pets swim. 

Volunteers collected 4 samples earlier this week from very obvious bloom areas and results from the Finger Lakes Institute indicate elevated levels of CyanoChlorophyll (blue green algae). This week we had our highest blue-green cyano level of the 2020 season, from a sample taken just north of Vine Valley (see photo). Below are the results from samples collected this week.

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).  

These results are telling us that these isolated blooms must be avoided. These particular blooms were not tested for toxins; however, based on previous data collected we know that Canandaigua Lake blooms with high levels of blue green algae may also have high levels of the microcystin toxin. Exposure to blooms and toxins can cause symptoms such as diarrhea, nausea or vomiting; skin, eye or throat irritation and allergic reactions or breathing difficulties. 

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) continue with their routine testing of the public drinking water for the presence of toxins associated with harmful algal blooms. So far there have been no detectable levels of toxin in the finished drinking water. Results from routine sampling can be viewed here:

We thank you all for your continued support and ongoing efforts to help us monitor and protect the lake. We hope you will check out the tips below for ways you can help keep nutrients out of the lake when doing that fall cleanup around your property in the coming weeks. Remember, excess nutrients may fuel algae blooms and aquatic plant growth! Homeowners are all stakeholders in our watershed health, so let’s do our part to reduce our collective impact. Our watershed will thank us.



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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