The recent discovery of zebra mussels at Christmas Lake in the west metro has prompted an aggressive response.

Christmas Lake has long been suspected to be vulnerable to a zebra mussel infestation, because it is so near to Lake Minnetonka, where zebra mussels were found in 2010.

In an attempt to keep Christmas Lake zebra-mussel free, the lake’s homeowners association and the city of Shorewood in recent summers hired a private company to inspect boats coming and going from the lake’s only public access.

The Department of Natural Resources successfully fought to establish the public launch site at the lake decades ago. But the site isn’t owned by the DNR. Instead, the city of Shorewood owns and operates it, with certain restrictions set by the DNR.

Joe Shneider, president of the lakeshore owners group, has said the landing would be closed until freeze-up. But Heidi Wolf of the DNR said Tuesday the agency will require the access to be reopened before then.

The Christmas Lake zebra mussels were discovered by the Minnehaha Creek Watershed District in a routine inspection. The mussels were young and concentrated near the boat landing, and the district, working with the lakeshore owners group and the DNR, has closed the access and cordoned off the water area nearby and will treat it with the biological agent Zequanox.

Zebra mussel expert Dan Molloy has been flown in from New York by Christmas Lake homeowners to help oversee the application. Molloy is credited with developing Zequanox. On Sunday, Molloy inspected the Christmas Lake shoreline and found no further infestations.

In laboratory tests of Zequanox, native fish and mussels weren’t affected by its application, said DNR research scientist Gary Montz. Instead, Montz said, it seems to target zebra mussels specifically.

“But whether it pans out as a successful treatment in a lake remains to be seen,’’ Montz said.

Zequanox is made from dead bacteria and has a short life in the environment. Zebra mussels die after eating it.

Other actions underway at the Christmas Lake landing include the removal and replacement of the ramp and dock, and the dredging of nearby rocks. Wolf said the access will be open when the construction is complete.