Zebra Mussels in Lake Minnewashta – Update and Proposed Rapid Response Plan

A meeting was held on 8/22/16 at the Minnehaha Creek Watershed District’s offices to review the discovery of zebra mussels in Lake Minnewashta and develop a Rapid Response Plan of attack. Representatives from the MCWD, Carver County, the city of Chanhassen, the MN DNR, Christmas Lake Homeowners Association and the LMPA attended and the spirit was very cooperative. The MCWD’s Aquatic Invasive Species Program Manager, Eric Fieldseth, led the meeting and provided the following information.

On August 18th, during a routine weekly check, four zebra mussels were found under one of the two piers at the Carver Parks boat launch on Lake Minnewashta. The following day, a team of people inspected a broader area of “Little Minnie” as well as 8 other areas of the lake. Ten additional zebra mussels were found near the launch but none were found beyond the public access. The mussels all appear to be juveniles but water samples were taken to see if infant mussels (veligers) were present. If found, that would indicate the mussels were reproducing. Those results are not yet available.

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. They like rock and weeds not muck.
3. It appears that only juveniles are present but we are awaiting the water samples
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 PROPOSED plan of attack was developed. Final actions, costs, approvals and timing are being worked but the proposal is 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 and may happen as soon as Wednesday August 24th. NOTE: This is a shallower launch than Access #1 so proper care much be taken especially with inboard and V-drive boats and some pontoon boats with bunk/fixed height trailers.

2. Purchase and install containment barriers in Little Minnie. The area to be contained is being finalized. Delivery and installation of the barrier may happen as soon as Wednesday August 24th. 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!

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.

The team is still working on finalizing the Rapid Response Plan including developing the eradication plans, securing agreement, approvals, materials and vendors and communicating our plans. The very capable leaders of the team are Eric Fieldseth from the Watershed District and Drew Dickart from Carver County’s Aquatic Invasive Species program. The LMPA offers them and the entire team our hearty thanks.

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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