Circle Lake group reports progress on weeds, but phosphorus problem persists

Dean Sunderland, chair of the Circle Lake Improvement District, told the Rice County Committee of the Whole on Sept. 1 that recent treatment work and a pilot restoration program have reduced invasive weeds and improved lake use for residents. “I'm getting a lot of phone calls from residents saying that, they've been able to use the lake, much more than than normal,” Sunderland said as he summarized the season's work.

Sunderland described a spring survey and DNR-permitted herbicide treatments that covered just over 91 acres and produced a strong post-inspection kill of curly-leaf pondweed. He also presented a bathymetry study and an array of aeration systems and continuous dissolved-oxygen and temperature sensors deployed to measure the pilot project's effects on bottom oxygen and sediment consolidation.

While aeration and other small-scale interventions have shown encouraging dissolved-oxygen swings compared with past years, Sunderland emphasized that phosphorus remains elevated. “Past studies of the lake have found that the phosphorus level in the lake is quite high,” he said, and the district is investigating whether binding or exporting phosphorus — including timed storage and discharge with DNR coordination — could reduce the in-lake load.

Commissioners asked technical questions about alum treatments, carp disturbance and biological additives. Sunderland said alum capping likely would not be effective because Circle Lake is shallow and common carp disturb caps, and that export or alternative binding strategies are under consideration. He warned the pilot is ongoing and that any measurable consolidation of muck will take several years. The district does not yet have a single treatment that solves the problem and plans to continue monitoring and testing.