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Cdg Lake Water Quality Update


Friday, July 14 2023

We kick off this summer’s first Weekly Water Quality Report with a review of this week’s significant flooding event, and an update on the the most recent water quality. This report was provided by Canandaigua Lake Watershed Council Watershed Program Manager, Kevin Olvany.

The storm of Sunday, July 9th, 2023 will long be remembered for the devastation that it caused within parts of the Town and City of Canandaigua, along with some neighboring communities. Over 5 inches of rain fell within 3 hours in some parts of Canandaigua near the Airport and County Road 32. Thanks to all the reports submitted by community members, we were able to document that other areas of the Town and City of Canandaigua received anywhere from 2- 4+ inches of rain.

If you were watching the radar and/or out in the storm, the rain just kept coming in waves of major intensity with little to no break between the waves. Gorham and Hopewell received anywhere from 1-3 inches of rain over a 1- 1.5 hour timeframe. When you look at the extreme precipitation tables for different storm durations- the areas in Canandaigua that had the 5+ inch totals exceed the 500-year storm event levels. The other areas in the Town and City were in the 50-100 year storm event levels. If that were not enough, we had 50-100 year storm events primarily in the Gorham and Hopewell area on June 12th and July 1st. July 3rd was a rain event that hit some areas like Onanda Park very hard. Onanda Park lost its walking bridge that goes across Barnes Gully in the lower park.

With all that has happened over the last month (plus the April 5th storm that caused significant flooding in certain areas), we have seen tremendous amounts of runoff from the watershed entering the lake. After the major flood event of Sunday and the resulting disaster declaration, the beach operators of Onanda, Butler, Kershaw, and Deep Run beaches have been sampling for E. coli bacteria. E. coli bacteria is an indicator bacteria for the potential of various pathogens in the water that can cause human illness. Bacteria and pathogens primarily come from the intestines of warm-blooded animals.

The scientific literature documents that the main sources of bacteria are urban runoff, sanitary sewer cross-connections, agricultural runoff along with animals living in the natural environment. The NYS Department of Health (DOH) sets a standard of 235 colonies of E. coli per 100 mL. All of the regulated beach areas were well above this threshold when we tested on Monday and received the results on Tuesday. Press releases were put out to inform the public that the beaches were closed. Samples were then collected on Wednesday and all beaches were substantially lower with Onanda, Deep Run, and Butler beaches being below the 235 threshold and Kershaw was slightly above it. We tested again on Thursday and the wind patterns played an important role in the results at Deep Run and Kershaw. One of the two samples at Deep Run exceeded the 235 E. coli count and Kershaw was also above the 235 E. coli regulatory threshold. There was a south/southwest wind that was concentrating the turbid water into the Deep Run area along with Kershaw. Onanda and Butler and the second Deep Run sample taken from the north swim zone were well below the threshold. Tests were collected today at Deep Run and Kershaw and the lab will provide results tomorrow (Saturday). The beaches visually looked better today than they did yesterday.

What does all this mean for the lake and recreating this weekend?

The good news is that we are seeing the E. Coli levels substantially decreasing overall throughout the week. Some beaches are reopening. There are natural processes in place in the lake ecosystem that are causing the bacteria to reduce substantially. There seems to be a good correlation between visual turbidity in the water (brown-looking) and E. coli levels. This is not surprising as the runoff from urban and agricultural areas are the primary drivers of E. coli levels. This is a natural ecosystem with many variables so you can never have zero risk- but the risk tends to be lower in clear water.

We also tested for blue green algae (cyanobacteria) off-shore from the beaches and the test results showed no blue green algae (cyanobacteria). Reports from the CLWA shoreline volunteers and Secchi disk volunteers are a valuable contribution to the overall monitoring efforts with watershed staff and researchers. Secchi disk reports coming in this week documented a significant decrease in clarity, an average of 3.3 meters. This is the lowest reported weekly average since the last week of August in 2017.

These have been huge precipitation events. In my 25 years of working here along with conversations with highway superintendents and long term residents this has been a unique rain year. I saw one news report on the weather channel that talked about the dual impacts of Climate Change and El-Nino potentially super charging these storm events. It sure feels that way. The local, county and state highway departments are hard a work trying to fix the damage in their road systems. Collectively, we are looking to partner with interested landowners to see if we can build more water quality and quantity resiliency into the watershed in order to reduce the magnitude of these extreme events. We can’t build infrastructure big enough for some of these events. We all have to do a better job of finding ways to build flood storage into the system and not build structures in flood prone areas.

Have a fun and safe weekend.

Canandaigua Lake Watershed Association

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