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The Lake Where You Live: Window to your lake

January 17, 2020 by Ted Rulseh

How clear is your lake? Is it getting clearer or less so with time? What is its trophic state? How deep is it at the deepest point? What’s the acreage?

Maybe you know some or all of this already, but if you don’t and you’re curious, there are easy ways to answer the questions. An abundance of data about Wisconsin lakes can be found in a few minutes online.

The first stop is the website of the Citizen Lake Monitoring Network (CLMN) at https://dnr.wi.gov/lakes/clmn. This is a network of volunteers — not scientists, just ordinary folks — who regularly take measurements of water clarity, dissolved oxygen, phosphorus, chlorophyll and other parameters on the lakes where they live.

All that data is collected and archived for use by anyone from Department of Natural Resources staff members to curious lake residents and visitors. For the curious there’s a wealth of information to be found.

Take Birch Lake, where I live. At the main page I click on Oneida County, where the lake is (about 15 miles southeast of Minocqua). That brings up a list of more than 100 lakes the network monitors. From the list I choose Birch and click on “details.”

There I find year-by-year data on water clarity as measured by a Secchi disc. This is nothing new to me because I’m the citizen volunteer who does the clarity readings about a dozen times a year from May into October. I can call up a graph of clarity information from all the years that I and my predecessor volunteers submitted data.

The graph shows that for July and August, the average Secchi disc reading has been about nine feet (in simple terms the depth to which a black-and-white the disc sinks before it can no longer be seen). The data for 2019 shows that the average July/August reading was 11.1 feet, a fair bit better than for the average year.

During that period the water color was reported as clear and brown. This suggests that the Secchi depth may have been mostly influenced by tannins — stain from decaying matter that is natural and not a sign of pollution. The lake’s Trophic State Index, based on the Secchi data, was 42, suggesting that the lake is mesotrophic, containing a moderate amount of nutrients. 

For comparison, I check a different lake (which shall remain nameless) where I like to fish. It says the average July/August Secchi reading was 22.46 — very clear indeed, and in line with what I have observed. The Trophic State Index puts the lake in the oligotrophic range, meaning poor in nutrients. This lake was also sampled by a volunteer for chlorophyll and phosphorus.

For more basic information about your lake, you can just enter its name in a search (in my case: Birch Lake Oneida County Wisconsin). This leads to a DNR page that gives the lake’s size (198 acres) and maximum depth (27 feet). It also lists the fish species present and the lake-specific fishing regulations (size and bag limits).

Here in the middle of winter it’s fun to poke around these online resources and learn more about your own and other favorite lakes.

Ted Rulseh resides on Birch Lake in Harshaw and is an advocate for lake protection and improvement. His Lakeland Times and Northwoods River News columns are the basis for a book, “A Lakeside Companion,” published by The University of Wisconsin Press. Ted may be reached at [email protected].


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