The lone, mysterious zebra mussel that turned up in Lake Harriet last fall now resides in a freezer belonging to the Minneapolis Park and Recreation Board.
Debra Pilger, whose career is dedicated to protecting the City of Lakes from aquatic invasive species and other environmental harm, remembers the shudder she felt when the 2½-inch-long critter was discovered Sept. 8 on a discarded, submerged sailboat cover. Similar discoveries in more than 100 other Minnesota lakes have been forerunners to dreadful infestations.
"It was at the end of the day and they brought it to the office,'' Pilger recalled. "It was a depressing Friday.''
Cleanup volunteers from a local scuba club found the boat cover, along with other trash, in shallows just east of the Lake Harriet Bandshell. A city watercraft inspector checked over the junk and sounded an alarm that's still reverberating.
In an interview last week, Pilger said her division of the Park and Recreation Board will intensify efforts to stop zebra mussels. Under a beefed-up action plan first written seven years ago after Lake Minnetonka became infested, the city will search more often and more extensively for zebra mussels. Crews also will screen the water periodically for microscopic larvae of the mussels.
Channels connect Lake Harriet to Lake Calhoun and Lake of the Isles. If zebra mussels took hold in any one of those lakes, public recreation and the overall ecology of those waters would be greatly devalued, Pilger said. The mussels multiply rapidly by millions and billions and their sharp shells cut into the feet of waders and swimmers. The striped mollusks upset the food balance in lakes by eating huge amounts of plankton otherwise available for fish to eat. Zebra mussels filter massive amounts of water, but subsequent gains in water clarity can be offset by stinky mats of algae that the mussels are capable of producing.
"There's no great solutions if they get in,'' Pilger said.
Keegan Lund, aquatic invasive species specialist for the Minnesota Department of Natural Resources, said the finding of a lone zebra mussel in Lake Harriet last year kicked off the largest-ever search for zebra mussels in Minnesota for detection purposes. Scuba divers, snorkelers and walkers turned over rocks, inspected aquatic plants, looked at boat hulls and checked all 200 mooring lines in the lake. They found zilch.