DETROIT LAKES, Minn. (AP) — The Minnesota Department of Natural Resources says it will be at least two years before the agency knows whether a pesticide applied to a northern Minnesota lake has killed a zebra mussel infestation.

It’s the first time the DNR is attempting to reclaim a lake from the aggressive mollusks. A pesticide commonly used to treat lakes for swimmers’ itch, copper sulfate, is being applied to a portion of Rose Lake near Detroit Lakes. The pesticide will be applied at least three times this fall and possibly again next year.

DNR invasive species specialist Nathan Olson tells Minnesota Public Radio the zebra mussels arrived in the lake because an individual moved a boat lift, with mollusks attached, into Rose Lake. That move could result in a $500 fine.

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