Take-a-Dip Secchi Disk Water Clarity Monitoring

By Dee Crofton & Lindsay McMillan

Have you ever been out enjoying a day on the lake and seen someone reeling in an odd-looking black and white disk from the side of their kayak, rowboat, or motorboat and wondered ‘what the heck are they doing?’ You are likely observing one of the many volunteers for CLWA who are performing a vital service to help monitor the quality of the lake that we all love and enjoy. What they are using is a device called a Secchi Disk.

The secchi disk was developed in 1865 by Pietro Angelo Secchi to monitor turbidity in the Mediterranean Sea. It was originally all white. In 1899 George C. Whipple modified it to what is in use today, a disk divided into black and white quadrants, 12” in diameter. 

Secchi disks are a simple, inexpensive tool used to measure the clarity of the water. A high secchi disk reading means that the volunteer can see further down into the water column – indicating good clarity. In winter and early spring, it’s not unusual to have incredibly clear water – sometimes as high as 12-14 meters! As summer progresses, clarity tends to drop and we experience lower readings and increased turbidity. Factors that might affect water clarity might include an influx of sediment from land use activities in the watershed after rain events, as well as increased algal productivity (phytoplankton) throughout the summer. 

In 2022, CLWA volunteers routinely monitored 16 sites on Canandaigua Lake, tracking weekly changes in water clarity. The strength of this volunteer network allows for fairly consistent reporting of lake conditions in real time. Secchi disk volunteers are some of the first to report a drop in clarity, which notifies us that conditions may be setting up for an impending cyanobacteria (HAB) bloom.  

2022 was considered a “light” year for cyanobacteria blooms, and the weekly average secchi disk data supported these findings, with readings ranging from 4.5-6.0 meter readings throughout July and August with no major significant drops in clarity.  However, digging into the data, we see that we did experience a drop in mid-July around the time of reported rain events (bringing more runoff into the lake system), as well as a consistent decrease in clarity throughout the month of August, which culminated with our first reported cyanobacterial bloom on August 16th (large localized bloom), followed by another on August 22nd (small localized bloom). See Figure 1. 

Figure 1

This volunteer data is imperative to the overall monitoring efforts on Canandaigua Lake, and is used daily by the Canandaigua Lake Watershed Manager, Kevin Olvany, and Association Director, Lindsay McMillan to help draft water quality updates that are sent in our community each Friday. If you aren’t already receiving the reports, sign up by visiting the CLWA website and clicking “sign up for e-news”. 

We want to thank our current secchi disk volunteers for their commitment to the health of the lake: Amy Bowen, Dee Crofton, Rob Gray, Nadia Harvieux, Scott Hill, Gary and Pam Helming, Bruce Kennedy, Alan Krautwurst, Scott Kreher, Marty Lasher, Joel Pasternack, Brian and Dolores Perkins, Kathy Postma, Lynn Thurston, Wade Sarkis, and  Bill Yust. Many have been with the program since its inception in 2014! 

As we look to the future of the program, there are exciting prospects on the horizon. In 2022, we added a new component where several of our secchi disk volunteers are also tracking water temperature at one-meter intervals to look at how the thermocline changes over the summer (See article, page xxx). In addition, the long-term data set from this program is used by researchers at SUNY Environmental Science and Forestry to train remote-sensing technology. More to come in the future!