Lake Minnewashta Zebra Mussel Eradication Work Nears a Successful Completion

Eric Fieldseth, from the Minnehaha Creek Watershed District, reported today that 100% of the Zebra Mussels exposed to the Copper Sulfate treatment in the last 10 days have died. These were mussels placed in contained cages and used to signal the successful completion of the treatment. No further chemical treatment is planned but the containment barriers will remain up for the weekend to allow a little more time in case any zebra mussels outside of the cages were alive. The containment barriers will be removed by Carver County early next week and the launch will be reopened at that time.

Note that beyond the initial 14 zebra mussels found, the MCWD spent two full days looking around the lake with SCUBA divers and snorkelers. No additional mussels were found outside the contained area. Based on the size distribution of the zebra mussels found (varying sizes ranging from 3 mm to 13 mm), and the fact that they were all found in 1 to 2 feet of water directly under the dock at the public access, and we never detected any veligers (baby/immature mussels) through our sampling, we don’t believe there is reproduction occurring in the lake. The best we can do is go off of the facts we have.

Now we really need all of the lakeshore owners to check their docks and lifts as you take them out this fall and carefully look for zebra mussels. If anyone would like to let the MCWD take a look at them as they are taken out, that would be great! Please email Jill at or Eric at if you are willing to let them look over your docks and lifts as they are removed.

The MCWD will conduct more surveys next spring looking for any additional signs of zebra mussels. Let’s hope they find nothing.

Three final points.
First, this was a very rapid and well coordinated effort by a lot of people. Special mention and thanks go to Eric Fieldseth at the MCWD for taking the lead and spearheading this. Speed was very important in this and Eric did an outstanding job.

Second, without the financial contributions of the MCWD (about $10,000), Carver County (about $10,000) and the Lake Minnewashta Preservation Association members (About $15,000) this effort might not have occurred. Without rapid containment and treatment, the results could have been disastrous as that would have allowed zebra mussels to infest broad areas of the lake with negative effects.

Finally, The LMPA members voted two years ago to build up an emergency fund for just such a purpose and thankfully we had it. Now that account is completely empty and we need to refill it. Please consider a generous donation in our fall fundraising campaign to make that happen. State, County and watershed funding on Aquatic Invasive Species efforts unfortunately are being severely curtailed and it will be up to the lake association members to carry a larger load in the future. Feel free to contact our local county commissioners to voice your concerns. Tom Workman,, is our county commissioner and he is a friend of Lake Minnewashta.

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