Zebra Mussels Discovered in Lake Minnewashta (Again) – Rapid Response Plan Being Worked

On September 21st, staff from Carver County, MCWD and MN DNR performed a zebra mussel search in Lake Minnewashta.  This was the third in-depth search of the lake this season.  A search in June found one adult zebra mussel at the public boat launch in Caver Park but a follow-up search in July found no zebra mussels. There are also weekly checks of a sampler plate at the public access and nothing has been found this season.  During this latest search, four zebra mussel juveniles were found under one of the two piers at the Carver Parks boat launch on Lake Minnewashta. Numerous other areas of the lake were checked that day, and no additional zebra mussels were found.

This discovery is disappointing and highlights the need for careful attention to cleaning, draining and drying your watercraft and gear before launching.

There is some good news.
1. The mussels were found only in the public areas.
2. The channel connecting Little Minnie to the rest of the lake offers a very poor substrate for mussels to adhere. Mussels like rock and weeds not muck.
3. It appears that only juveniles are present but we are awaiting the water sample results
4. It appears to be a recent introduction. As a reference, when Christmas Lake reported their mussel problem, they saw over 5000 in their sample. We caught it early.
5. Conditions are such that containment and treatment are a reasonable option.

Christmas Lake’s experience in 2014 offered some valuable lessons on Rapid Response
1. Immediate response is needed
2. Treat a much larger area than when you found them
3. We’ve learned a lot on what products can be effective at killing them without harmful side effects

A meeting is being set up to review the discovery of zebra mussels in Lake Minnewashta and develop a Rapid Response Plan. Representatives from the Minnehaha Creek Watershed District, Carver County, the city of Chanhassen, the MN Department of Natural Resources, Christmas Lake Homeowners Association and the LMPA are invited. The MCWD’s Aquatic Invasive Species Program Manager, Eric Fieldseth, will lead the meeting. Based on last year’s discovery, we expect to propose and deploy a similar action. Final actions, costs, approvals and timing need to be worked out but the proposal will likely be to:

1. Close Carver Park’s Boat Access #1 and reopen Boat Access #2 . Access #2 is to the left of the Public Beach as you are looking to the water. This may prevent transporting zebra mussels from Little Minnie to the larger section of the lake. NOTE: This is a shallower launch than Access #1 so proper care must be taken especially with inboard and V-drive boats and some pontoon boats with bunk/fixed height trailers. The date of closure will be announced well in advance in case residents want to get their watercraft out before it is closed.

2. Reuse the containment barriers purchased in 2016 and install in Little Minnie. The area to be contained is being finalized. Delivery and installation of the barrier is to be determined but this effectively closes that launch and all boat traffic into and out of the lake will take place at Launch Access #2.

3. Once contained, work the next steps of the process to eradicate the zebra mussels. This is the hard part! Last year we applied a chemical known as Earthtech QZ. We have a quantity left over which may be sufficient for our needs.

4. Ensure the zebra mussels have been eradicated, remove the containment barriers and reopen Boat Access #1.

5. Continue monitoring Little Minnie as well as our 10 existing monitoring stations around the lake to assure that zebra mussels are fully eradicated.
Residents who currently have monitoring plates in place should check them immediately and report any findings to the MCWD and Steve Gunther.

The team will be working on the Rapid Response Plan including developing the eradication plans, securing agreement, approvals, materials and vendors and communicating our plans this week and next.

Finally, although we expect that the MCWD and Carver County will provide a lot of the funding, the LMPA has offered financial support as well. Stay tuned and when a request for donations is made, please give generously.

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