Divers find 10 zebra mussels in Christmas Lake during follow-up search

Shorewood, Minn. — Several teams of divers extensively searched Christmas Lake for the presence of zebra mussels this week and found 10 of them near where the invasives were found last summer. 

The Minnehaha Creek Watershed District reports that the zebra mussels were attached to native mussels near the public boat access on the lake’s northern shoreline, just outside of the 0.6-acre area crews cordoned off and treated last the fall and winter. The divers did not find any mussels in the area that received treatment.

The search, which covered the entire shoreline up to 6 feet in depth, was conducted by crews from the Minnehaha Creek Watershed District (MCWD), the Minnesota Department of Natural Resources, Blue Water Science, and Waterfront Restoration on Wednesday and Thursday, May 20 and 21. The effort occurred about a month after an initial search of the area around the boat launch in the city of Shorewood turned up no sign of zebra mussels. 

“We’re disappointed by the discovery of these additional mussels,” said Eric Fieldseth, MCWD AIS Program manager. “However, we’re encouraged to see that no mussels were found in the treatment zone or beyond the immediate vicinity of the treatment area, and we’re exploring our options for addressing what appears to still be a localized infestation.”

An MCWD press release said the latest discovery shows the importance of closely monitoring an area after treating it. It also shows that there is usually no single solution – multiple treatments or hand-removal may be necessary over a longer period of time to fully get rid of an infestation.

The Minnesota DNR said the 10 zebra mussels were removed from the lake, and monitoring will be ongoing. The DNR will review all data collected and determine whether any further response is feasible and necessary.

“The follow-up searches suggest that the treatment in the Christmas Lake public access area was effective in eliminating mussels from the area,” said Keegan Lund, DNR aquatic invasive species specialist. “Unfortunately, we found zebra mussels outside the treatment area. These zebra mussels have probably been attached to native mussels in the lake since last summer or fall.” 

Divers found 10 zebra mussels in Christmas Lake just outside the area that was treated with chemicals including these two zebra mussels that were attached to native mussels.Following the initial discovery of zebra mussels at the boat launch last August, MCWD and the DNR worked together to contain the area around the launch and apply Zequanox, a non-chemical treatment used to kill zebra mussels. That application was followed by a copper treatment of EarthTec QZ in October and November. In December, a contractor working with the DNR injected 1,000 pounds of potassium chloride (potash) under the ice near the public boat access. It was only the third time potash was used for zebra mussel control in the United States. The applications of potash and EarthTec QZ were experimental, off-label uses requiring special emergency permission.

Crews will continue to closely monitor Christmas Lake throughout the year. MCWD staff will check the zebra mussel sampler at the boat launch each week, monitor the lake for zebra mussel larvae (“veligers”), and will use snorkel gear to search the shoreline in several locations around the lake in July and September. MCWD has developed a five-year monitoring plan for the lake to determine whether zebra mussels were completely removed.

In its Friday release on the infestation, the DNR noted that the treatment in the public access area of Christmas Lake in the city of Shorewood was one in a series of rapid responses by the DNR and other partners that have targeted small, isolated, and recently detected infestations of zebra mussels. Previous rapid response treatments of isolated infestations in other lakes have produced mixed results. Information gained from these treatments and searches will help the DNR determine when, where, and how to treat new zebra mussel infestations most effectively.

To that end, the DNR will be considering pilot projects to manage newly detected, isolated zebra mussels in other bodies of water this season. An assessment framework has been developed and more information will be gathered as the pilot projects are initiated. Lund stressed that pilot projects are only feasible for small, isolated infestations of zebra mussels that are detected early.  

Zebra mussels are an invasive species that can crowd out native mussels and compete for food sources with other aquatic animals such as larval fish. They attach to boat hulls and other water-related equipment and can create a hazard for swimmers due to their sharp shells. 

For additional updates on the aquatic invasive species or zebra mussel response effort at Christmas Lake and the District’s AIS Early Detector program, www.mndnr.gov/ais or  www.minnehahacreek.org/ais

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