Ever since zebra mussels infested Lake Minnetonka in 2010, Minneapolis officials have been bracing themselves for the discovery of the sharp-shelled invaders in one of the city's beloved lakes.
This year, the Minneapolis Parks and Recreation Board put forth its most expansive — and expensive — effort yet to prevent zebra mussels from getting into the lakes. Every boat entering Lakes Calhoun, Harriet and Nokomis on a public boat ramp is inspected, and parks staff have placed monitoring devices in the lakes to learn of any possible infestations early.
'A PRETTY EASY RIDE'
But one way zebra mussels could travel to Minneapolis is simply by floating down Minnehaha Creek. Lake Minnetonka flows into the creek, and zebra mussels were found as far east as Edina last year. The creek eventually flows through Lake Hiawatha in south Minneapolis.
"It's a pretty easy ride for them to get a far distance in a short amount of time," said Eric Fieldseth, an aquatic invasive species specialist for the Minnehaha Creek Watershed District.
Fieldseth has been making regular checks along the creek as part of a three-year research project, starting at Gray's Bay Dam where Lake Minnetonka flows into the creek. This year's late, wet spring has caused high water flows, making it difficult to access some areas of the creek. But even in places Fieldseth found many zebra mussels last year, he hasn't found them yet this year.
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"It could be an instance of too high of flow. The more of the areas they go through that are rocky and turbulent, probably the less likely they'll survive a trip farther down the creek, but you just never know," he said.
Although Minneapolis' Lake Hiawatha has been labeled "infested" because of its hydrological connection to Lake Minnetonka, no zebra mussels have been found there yet. Park board staff check a device attached to the lake's fishing dock monthly for any signs of zebra mussels.
"We definitely would want to let the public know so they can help us in not spreading the zebra mussels to any other lake in Minneapolis or in the state," Debra Pilger, who directs environmental management for the park board, said last week as she pulled up a chain holding the monitoring device.
It had plenty of slugs, snails and mud on it, but no signs of zebra mussels.
The Minneapolis Park and Recreation Board approved a $160,000 budget for boat inspections this year, which covers 6 a.m. to 10 p.m. April 15 through Dec. 1. The budget for inspections is about 10 times what the park board spent in 2011.
A DISRUPTIVE NUISANCE
The inspections aim to keep out a variety of aquatic invasive species, but zebra mussels are considered the biggest potential nuisance: They multiply quickly, and dead shells cut swimmers feet and wash up on the shore, emitting a strong odor. They've also been blamed for disrupting the lake's natural ecosystem.
There is no proven way to get rid of zebra mussels once they've established themselves in a lake.
"We think we're in kind of a unique position to protect the lakes in Minneapolis due to the fact that there are only a limited number of public boat launches," Pilger said. "We don't allow motorized boats on our lakes, so we have this opportunity to really focus on the people using the lakes, get them educated, and maybe then there will be some controls developed."
One possible control option, a bacteria that kills zebra mussels, is still being researched. Pilger said officials don't know how long their extra efforts will be sustainable, but they hope researchers will be able to come up with some solutions before zebra mussels show up.
Officials at the Minnesota Department of Natural Resources said the lack of a proven control is why they've focused on prevention and education. Boat inspections are being conducted statewide, though they don't even come close to catching every boat. A DNR study shows it would cost more than $65 million a year to have mandatory inspections at every lake infested with zebra mussels. The state's total budget this year to fight all aquatic invasive species is about $8 million.
POSTPONING THE INEVITABLE?
With zebra mussels showing up in new lakes every year, some have argued that fighting them is a waste of money because they'll eventually be widespread. But Ann Pierce, who oversees the DNR's invasive species unit, said the efforts can also prevent new invaders from finding a home in Minnesota.
"There are some that are not here yet, and as our habitat changes, and as potentially things make it into our area or we have a changing climate as our winters change, we might see new things," she said. "I think we have a good opportunity for those we're not seeing right now, to get a better handle on them as they potentially come into the state."
On the fishing dock at Lake Hiawatha, Tyrone Gillam said he fishes in the lake about once a week and often brings his 4-year-old daughter and 2-year-old son to the swimming beach, where they like to go barefoot. Gillam said he's happy some of his tax money is going toward keeping zebra mussels out of the city's lakes.
"One thing about Minnesota is we are known for our lakes, and I think we need to keep our reputation with something like that," he said.