Update on Canandaigua Lake Blooms – October 4, 2023

On Monday, October 2nd, and Tuesday, October 3rd, Canandaigua Lake experienced a significant widespread cyanobacterial harmful algal bloom (cyanoHAB) event. Blooms were found along many shoreline areas- on the east side from Vine Valley north and the west side from Menteth Point north. There were also several open water areas experiencing blooms. All that “green” generated a lot of interest about water quality and as a result, we have had many new subscribers to our e-newsletter. Welcome to our new followers!

While we don’t often send out reports mid-week, we thought we’d share a follow-up to Monday’s water quality notification.


Between Monday and Tuesday, our trained cyanoHABs volunteers responded swiftly, providing 51 reports from around the lake. Seventy-four (74%) of reporters saw HABs in their area. We also had dozens of reports come in from the public, reporting areas of surface streaking, green-colored water, and surface scum. Volunteers collected 19 samples to track blue-green (cyano)chlorophyll and toxin levels and samples were sent to the Finger Lakes Institute yesterday. We just received the cyanoChlorophyll, which can be found below. Toxin results are not yet available.


Based on the above results, all but one of the samples collected had cyanoChlorophyll levels above the DEC 25 ug/L (micrograms per liter) threshold for a bloom. The one sample in the Cottage City area showed some of the highest levels we have recorded in recent years.

Our municipal partners acted quickly on Monday and roped off the public access areas where blooms were forming, as this is where pets and people swim. We thank them for their attention to this matter. The Canandaigua Lake Watershed Council has also been surveying shoreline areas and actively researching the migration of cyanoHABs throughout the water column.

Your “Need to Knows”.

While it is frustrating not to know when and where the blooms will be at any given time, we need to keep in mind that the lake is a living, changing ecosystem influenced by many factors, including wind patterns, water temperatures, weather, nutrient inputs, and impacts from invasive species. Read more about contributing factors here. Some areas of the lake may look pea-soup green, and others may be clear, as was the case this week. Remember: Lake conditions may change hourly. This means it is impossible to pinpoint when and where a bloom may pop up and where it will be “safe” to recreate. The best course of action for this is to educate yourself, your friends, and your family on what to look for and how to avoid it. While it is very hot and tempting to swim, please keep pets and people out of waters with visible signs of surface streaking or discolored, green water.

Today (Wednesday, 10/4) we have not had as many reports come in, although there are still blooms out there. Winds picked up slightly today, and surface waters are mixing. Secchi disk water clarity results also look good – we have not had a huge drop in overall clarity, which is promising.

Please continue to keep an eye out for signs of HABs as the sunny, warm conditions continue this week.

Please email HABs@canandaigualakeassoc.org with any questions.