Upcoming Treatment

Lake Riley will be receive a copper sulfate treatment to help control zebra mussels in late June - early July. Residents with shoreline who wish to opt-out of the treatment may contact Shelby Sterner at ssterner@rpbcwd.org or 952-607-6486.

View the Lake Riley Zebra mussel treatment flyer

 

The Problem with Zebra Mussels

The Zebra Mussel (Dreissena polymorpha) is native to Eastern Europe and Western Russia. The small mussels with striped, D-shaped shells live underwater and were accidentally released into the Great Lakes. First discovered in 1988, the invasive mussel has spread to several states including Minnesota.

Zebra mussels cause recreational, economic, and ecological damage. They attach to equipment such as boat motors, causing poor performance and costly repairs. Their sharp shells also pose a hazard to swimmers, who can cut their feet as they encounter zebra mussel-encrusted objects such as docks, rocks, and swim rafts.

The invasive mussels damage aquatic systems by outcompeting larval fish and other animals for food. They also attach to and kill native mussels. New reasearch also suggests that zebra mussels concentrate mercury near the lake bottom which can cause bottom dwelling fish to have increased mercury levels in their tissues which can have health affects to humans when they are consumed.

Treatment Overview

RPBCWD staff are partnering with researchers from the University of Minnesota’s Minnesota Aquatic Invasive Species Research Center (MAISRC)  ⬈to evaluate a copper treatment approach to managing a zebra mussel population. The study will take place on Lake Riley, located in Chanhassen and Eden Prairie, which has a well-established zebra mussel population first detected in 2018.

Complete eradication of an established zebra mussel population in a waterbody is unlikely. However, treatments with a copper solution have been shown to reduce the numbers of zebra mussels. The goal of this study is to evaluate control of zebra mussels with a low-dose copper solution treatment. Large amounts of copper may be toxic to aquatic life, but evidence shows that a low dose copper treatment may be effective against zebra mussels with limited impact to other species. A similar study ⬈ was performed by MAISRC on a bay in Lake Minnetonka in 2019.

Timeline

The zebra mussel control study began on Lake Riley in early summer 2025 with collection of data to assess existing conditions. Data collection focused on zebra mussel population density, distribution, and reproduction; macroinvertebrate, zooplankton, and phytoplankton abundance and diversity; water quality indicators such as chlorophyll-a; and copper level testing.

The copper treatment will be applied in late June - earlyJuly 2026 at the peak of zebra mussel reproduction. Following the treatment, researchers will collect data to monitor the impact to zebra mussels, non-target species, and water quality. Once completed, a summary of the study results will be made available to the public.