2018 Flathead Lake Secchi Dip-in

More than 60 kids, grandkids, high school and university students, and summer and local residents dipped Secchi disks into Flathead Lake in July as part of the inaugural Flathead Lake Secchi Dip-in to measure water clarity. The Flathead Lakers and the Flathead Lake Biological Station partnered to launch a new Citizen Science program. We are gratified to have so many people participate in our first project.

Citizen Scientists took 44 Secchi measurements all around Flathead Lake. The depth at which the Secchi disk remains visible when lowered into the water provides a measure of water clarity. The measurements ranged from 3.8 meters to 13.5 meters. The range of depths measured reflects moderate to exceptional water clarity. The graph shows how the 2018 Flathead Lake Secchi Dip-in compared to historical Flathead Lake data at mid lake deep and lakes around the United States.

Our Citizen Scientists observed an amount of variability in water clarity around the lake during a single week in July that equals the total variability observed at one site over the last 40 years by the Biological Station’s monitoring program. These results show water clarity around Flathead Lake is considerably more dynamic than Station researchers predicted. These results helped the Flathead Lake Biological Station argue the need to expand monitoring efforts to other areas around Flathead Lake, and lead to the new monitoring site in Polson Bay.

Volunteer citizen scientists also collected water samples. Since the Biological Station’s long-term monitoring program has been collecting samples at only one or two sites, analysis of samples from many locations provided new insights about lake water quality.

Nutrient concentrations varied across the lake, but were within the range previously observed. The most striking results were how similar calcium concentrations were around the lake. This means that there are likely no areas in Flathead Lake that offer protection from invasion by nonnative mussels due to a lack of calcium, which they need to produce their shells.

Citizen science sample sites

Our Flathead Lake Secchi Dip-in is part of the nationwide Dip-in started in 1994 by the North American Lakes Management Society. It is a great example of the potential of volunteer citizen scientists to gather useful data for understanding lakes.

We are grateful for the Greater Polson Community Foundation’s generous grant support to help launch our Citizen Science program, along with support from participants and Flathead Lakers members. Citizen Scientists will be dipping Secchi disks again next summer, contact Hilary Devlin at to get involved in our Citizen Science Program this summer.