Four clear-water records, read in context.
Compare published summer Secchi-disk summaries for four named Minnesota lakes—then check today’s official record before drawing conclusions about water quality or safety.
Compare the measurementsWhat a Secchi depth means
A black-and-white Secchi disk is lowered until it disappears from view. That depth is recorded as water transparency: a larger number means the disk remained visible deeper. Sun, waves, algae, suspended sediment, dissolved color, season, location, and observer conditions can all affect a reading.
These are historical mean-summer summaries quoted in Minnesota DNR reports that identify the underlying MPCA records. Their periods differ, so this is a comparison of published examples—not a current or complete statewide ranking.
Measurement periods are printed on every card. Reports and current tools checked July 27, 2026. Read the DNR Secchi method
A dated window into transparency
The bars use the same unit—feet—but the collection is intentionally unnumbered because monitoring windows differ. Open each report for sampling context.
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Ten Mile Lake
18 feet mean summer clarity
Cass County · DNR/MPCA ID 11-0413-00
Measurement period: 1974–2006
Open the official lake report -
Pleasant Lake
15 feet mean summer clarity
Cass County · DNR/MPCA ID 11-0383-00
Measurement period: 1983–2006
Open the official lake report -
Birch Lake
13 feet mean summer clarity
Cass County · DNR/MPCA ID 11-0412-00
Measurement period: 1990–2004
Open the official lake report -
Round Lake
13 feet mean summer clarity
Aitkin County · DNR/MPCA ID 01-0204-00
Measurement period: 2004–2013
Open the official lake report
Explore newer satellite-derived clarity in UMN LakeBrowser · Check lake records in DNR LakeFinder
Clarity is not the same as quality or safety.
Clarity describes how far light penetrates. Water-quality assessment also considers nutrients, algae and other pollutants against standards. Safety is more immediate and specific: harmful algal blooms, bacteria, fish-consumption guidance, weather, cold water, currents, ice, and local closures require their own current evidence.
Treat a clear view as an invitation to investigate—not permission to drink, swim, cross ice, or eat fish without checking the right current guidance.
