The Minnesota Department of Natural Resources says zebra mussels have been found in Gilbert Pit, an old mine pit in St. Louis County.
The DNR says it's the first time zebra mussels have been found in a mine pit lake, and the farthest north they have been seen in the state.
Adult zebra mussels were found about 250 yards from the pit's boat access.
The lake is known locally as Lake Ore-Be-Gone.
The DNR has urged boaters to prevent the spread of invasive species by thoroughly cleaning boats and trailers. That includes draining water from bilges and livewells and any other containers before leaving an infested lake.