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Clearly Superior

picture of lake with canoe

Five years of volunteer efforts to measure Lake Superior’s water clarity show it is remarkably clear; however, results can vary greatly in some locations. Photo by Michael Douglas

Once a month from May through November, Peter Van Straten of Duluth climbs into his sea kayak and paddles 120 strokes out into Lake Superior near Duluth. He checks the air and water temperature, and wind direction. Then, careful not to lean over too far in his kayak, he drops a white metal disk into the lake and checks the water clarity.

Farther up the shore, at Silver Bay, Eric Iversen heads out in his 21-foot fishing boat. He checks the water clarity at two spots--one off the shore near Silver Bay and the other near his cabin in Little Marais.

Both Peter and Eric are volunteers in the Superior Lakewatch program. For the past five years, 50 volunteers in Minnesota, Wisconsin, Michigan, and Ontario have been checking Lake Superior’s water clarity. Results of their efforts show that Lake Superior is remarkably clear, with visibility averaging 27 feet deep. However, clarity varies in different locations around the lake.

Organized by representatives of Sea Grant, local universities, and the Lake Superior Center, the Lakewatch program’s goal is to take one characteristic--water clarity--and measure it regularly over time in order to monitor long-term trends in the water quality.

Elaine Ruzycki, Minnesota Sea Grant Superior Lakewatch Coordinator, acts as organizer for the Minnesota section of Lake Superior shoreline. “Volunteers are the key to the Lakewatch project,” said Ruzycki. “They make it possible for scientists to accumulate long-term data from areas all around the lake.”

Secchi disk illustration

Prior to Superior Lakewatch, there were no international programs that collected routine, yearly data. Ruzycki trains volunteers to use a Secchi disk (“Secchi” rhymes with “Becky”). The disk is a round piece of white metal, 20 cm in diameter, which is tied to a 1/4-inch polyester line marked off at 2-foot intervals. A volunteer lowers the disk into the water until it disappears. Then the disk is raised slowly until it is again visible. The depth at which it reappears is recorded. At the end of each summer, volunteers send their data to Elaine. She compiles it and sends it to Project Coordinator Jay Sandal at the Lake Superior Center, where the information is added to a basin-wide data set that will help scientists distinguish changes in water quality over time. Over the last five years, Superior Lakewatch volunteers have recorded 1,700 Secchi disk transparency measurements.

The Secchi disk is a simple way to measure water clarity. The cloudier the water, the shallower the depth at which the Secchi disk disappears from view.

In clear water, Secchi readings are usually high. Measurements can vary depending on wind direction and time of year. Sometimes wind can transfer or stir up sediment from river mouths or the lake floor. Or it can improve water clarity by upwelling clear water from the center of the lake. In the summer, algae growth is another cause of cloudiness.

Iversen joined the Superior Lakewatch program because data gathering seemed like a good way for him to be part of the Lake Superior community. “As a volunteer I don’t really understand the true scope of the data we’re collecting,” Iversen said. “But I recently attended a meeting where many of the scientists involved in the program were discussing the project, and I realized the data I collected is an important part of what these scientists were talking about.”

Van Straten vowed when he moved to Duluth that he “never wants to take this area for granted--it’s so beautiful.” Collecting Secchi disk readings gets him out to enjoy the lake and gives him a way to help monitor the health of the lake.

The Superior Lakewatch five-year report was recently published by the Lake Superior Center. To obtain a copy of the report for a small fee, contact Jay Sandal at 218.720.3033. To volunteer for Lakewatch, contact Elaine Ruzycki at 218.720.4337.


By Nancy Nelson
March 1998

Return to March 1998 Seiche



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