Water Quality

2025 Aquatic Plant Survey Highlights Growing Concern Over Starry Stonewort

Grant-funded monitoring shows healthy native plants, low watermilfoil levels, and increasing starry stonewort in Pine and Grass Lakes. 

The Cloverleaf Lakes 2025 Point-Intercept Data Summary Report, prepared by Onterra, LLC, presents the results of aquatic plant surveys conducted on Round Lake, Grass Lake, and Pine Lake on July 28, 2025.  This work is part of an ongoing Wisconsin DNR Aquatic Invasive Species Early Detection and Response grant, which supports long-term monitoring of lake health and invasive species in the Cloverleaf Lakes system.

The 2025 survey shows that the lakes continue to support a strong and diverse community of native aquatic plants, an important indicator of overall lake health.  Eurasian and hybrid watermilfoil, historically a primary concern, were found at low levels across all three lakes, continuing a natural decline that began in 2024.

Starry stonewort is currently the most significant concern.  First detected in Pine Lake in 2021, starry stonewort has continued to expand and was found at approximately 15 percent of surveyed shoreline locations in 2025.  It has also increased in Grass Lake, where it now occurs at nearly 10 percent of surveyed locations.  Starry stonewort has not been detected in Round Lake, which remains free of this invasive species.

Starry stonewort is particularly challenging because there is currently no proven, long-term treatment that effectively controls or eradicates it.  Chemical treatments have shown only short-term suppression, making prevention of spread the most effective management tool.  Starry stonewort spreads primarily by hitchhiking on boats, trailers, anchors, and other equipment moved between lakes.

Lake users and property owners are encouraged to remove all plants and debris from equipment, drain water from boats and gear, and allow equipment to fully dry before entering another lake.  These actions are critical to protecting Round Lake and slowing the spread within Pine and Grass Lakes.

Ongoing monitoring through this grant-funded program will continue to guide management decisions and help protect the long-term health of the Cloverleaf Lakes.