Lake Minnewashta zebra mussel treatment appears successful!

100 percent mortality after application of copper product
Wednesday, September 28, 2016

Following a multi-agency response to the discovery of zebra mussels in a Lake Minnewashta bay, initial results indicate the treatment was effective. The 29-acre bay known as “Little Minnie” was treated with the copper product EarthTecQZ after a small number of zebra mussels were found at the public boat access in August. The treatment appears to have killed 100 percent of the mussels within 10 days of its application.

“These results are encouraging,” said Eric Fieldseth, Minnehaha Creek Watershed District (MCWD) Aquatic Invasive Species (AIS) Program Manager. “We applied lessons learned in a similar response at Christmas Lake and we are hopeful this initial successful outcome will hold.”

MCWD’s aggressive early detection program led to the discovery of 14 juvenile zebra mussels at the Lake Minnewashta public boat access on August 18. The treatment plan, developed by a joint partnership of the MCWD, Carver County and the Lake Minnewashta Preservation Association in coordination with the Minnesota Department of Natural Resources (MN DNR), focused on the entire bay where the access is located. The 29-acre bay is three times the size of an area treated at Christmas Lake in 2014, which was deemed too small after zebra mussels were found outside the zone. The Lake Minnewashta response is the largest known open water treatment for zebra mussels in the state of Minnesota.

“By broadening our response well beyond the spot where the zebra mussels were found, we improved our chances for success,” said Fieldseth. “We learned from Christmas Lake that you need to treat the largest area feasible and we are pleased we were able to do that.”

The copper product in Lake Minnewashta was used at a much lower concentration than the Christmas Lake response, which saved costs and helped reduce non-target impacts.  

Subsequent monitoring of the rest of the lake over the next few years will be necessary to confirm whether zebra mussels are present in other areas of the waterbody. Staff from Carver County, MN DNR and MCWD will continue closely monitoring for zebra mussels next spring, as part of the DNR’s requirement to make annual monitoring reports for the next three years. Lakeshore property owners can help by looking for zebra mussels as they remove their watercraft, docks and other equipment from the water this fall.

“Information from homeowners is a key factor that will help us determine the long-term success of this treatment,” said Andrew Dickhart, Carver County AIS Coordinator. “We encourage them to be vigilant as they prepare their boats and other water-related gear for winter.”

The barriers that cordoned off the treatment areas have been removed. The public boat access, which had been closed during the treatment, is now back open to the public.

Carver County AIS boat inspectors routinely check boats at the Lake Minnewashta public access for zebra mussels and other invasive species. Since 2012 inspectors have completed nearly 19,000 checks at Lake Minnewashta and on 15 occasions have stopped watercraft with zebra mussels attached. 

Zebra mussels attach to boats, lifts, and other water-related equipment, and they also attach to aquatic plants. They can survive out of water and be spread from one water body to another. Microscopic larvae (veligers) can survive in water contained in bait buckets, bilges, ballast bags or any other water moved from an infested lake or river.

In Minnesota, you must take the following steps to prevent the spread of zebra mussels:


  • clean weeds and debris from your boats, and remove any attached zebra mussels,
  • drain your boat, livewells, and baitwells, and keep all drain plugs out while traveling,
  • dispose of unwanted bait in the trash, and
  • dry docks, lifts, swim rafts and other equipment for at least 21 days before placing into another water body.


More information on AIS prevention and management is available from and Carver County’s AIS Program.