The slow but insidious spread of zebra mussels into more Minnesota lakes and rivers continues, with the Department of Natural Resources confirming Tuesday that the invasive mussels have invaded Lake Ore-Be-Gone in Gilbert.
After a report of mussels in the former iron ore mine that's now a popular fishing lake, DNR divers confirmed adult mussels had infested an area near the lake's boat landing.
This is the first time zebra mussels have been found in a mine pit lake and the farthest north they have been found in Minnesota.
In the Northland, only Pike Lake near Duluth and Lake Superior and the St. Louis River estuary in the Twin Ports are known to be infested with the invasive mussel.
"It's a reminder that invasive species can keep moving north. We need to be vigilant," Rich Rezanka, DNR invasive species expert in Grand Rapids, told the News Tribune.
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It's not clear how the mussels got into Gilbert Pit Lake, although the 223-acre lake is popular with visiting scuba divers and trout anglers -- both groups of which also may frequent infested waters of Lake Superior.
Doug Jensen, invasive species expert for Minnesota SeaGrant in Duluth, said zebra mussels can spread through a range of activities, from moving docks to waterfowl hunting to diving and fishing.
"Not to point fingers, but everyone using the lake has to take precautions," Jensen said.
It's also not clear why only large zebra mussels were found, but it could mean that cold, clear, deep lake is not great for mussels to grow.
"Reproduction may not be as effective as it is a little more south like Brainerd and Lake Mille Lacs," where the mussels have invaded many lakes and exploded in number, Rezanka said. "But we really don't know why."
DNR divers have found up to 8,000 zebra mussels per square foot in some places on Mille Lacs, according to Rezanka. But their impact on the lake's ecosystem remains unknown.
"Clearly the nutrients are there for them to thrive and reproduce, and those nutrients they use aren't available to the natural system anymore. But we haven't seen any big impact on fish. At least not yet," he said.
Boaters, anglers and divers who use Lake Ore-Be-Gone are urged to be extra-thorough when decontaminating their boats, trailers, anchors and other equipment when leaving the water. State law makes it illegal to move live fish or water out of infested lakes.
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The mussels can't move on their own, but move with currents or are moved -- usually accidentally -- by people. They attach themselves to any smooth surface under water and feed by filtering nutrients out of the water.
Zebra mussels, native to Europe, are believed to have moved into the Great Lakes in the ballast of oceangoing ships. They first were found in Minnesota in the Duluth harbor in 1989 and then began to explode in numbers in the Twin Ports harbor by 1998. They also have moved north into Minnesota through the Mississippi River system and have been moved by humans into several Twin Cities, western and central Minnesota waterways.
Boaters should:
