After additional searches by multiple agencies turned up a second zebra mussel in Lake Sylvia on Tuesday, June 21, the lake is now officially considered infested with the invasive species.
That makes Sylvia the third area lake to have a confirmed zebra mussel presence. Clearwater Lake became the first where zebra mussels were discovered last July, and the invasive species was discovered in Lake John in September. After the Lake John discovery both Sylvia and Cedar were also searched last fall, but no zebra mussels were found at that point.
Staff from Anchor Dock and Lift discovered the first zebra mussel in Sylvia on Monday, June 13, attached to weeds in about 15 feet of water at the southernmost part of the east lake.
That finding was reported to the proper agencies, and the Minnesota Department of Natural Resources, the Minnesota Conservation Corps, Blue Water Science and volunteers from the lake association gathered to perform snorkel and shoreline searches last week.
Christine Jurek of the DNR said that the searches were confined to the south and southwest shores of east Lake Sylvia, so finding just one additional mussel wasn’t unusual.
"It’s likely that if searches were continued that perhaps more zebra mussels would be found," she said. "We did a subset just to confirm the presence in Lake Sylvia.
We didn’t do any distribution or abundance type surveys."
Steve McComas of Blue Water Science echoed that thought.
"The odds are that there are other zebra mussels in the lake. It’s a big lake, and boy, it’s a needle in a haystack," he said.
The second zebra mussel found was about one centimeter in size and was discovered by snorkelers on a rock located off a point some distance up from the south shore. Jurek said that there are general size guidelines, but declined to speculate on whether the mussel was an adult or a juvenile. Both could be present in the lake, she said.
Chris Hector, president of the Greater Lake Sylvia Association, said that it appears the zebra mussel population is limited, at least for now.
"There aren’t that many of them. We had over 20 people out looking for the better part of a day," he said. "But based on that, the DNR officially considers us an infested water, and has posted signs at the ramp to that effect."
Hector said the development is disappointing for the lake association, which has been one of the most proactive in the area in terms of establishing a monitoring program to check boats for zebra mussels at public access points. In 2014, inspectors turned away one boat at an access that was carrying fully grown zebra mussels. In spite of those measures, this month’s discovery was far from a shock.
"It’s not unexpected. In other words, we kind of went into this with our eyes wide open," said Hector. "Our goal was to do everything that we could (to prevent the entry of zebra mussels), recognizing that it’s kind of an uphill battle."
Furthermore, Hector said that the efforts made toward preventing the spread of zebra mussels remain important to carry on, because zebra mussels are not the only invasive species menacing the Heart of the Lakes. Others that have become an increasing concern include spiny waterflea and starry stonewort.
"Our feeling is that we’re not going to stop trying to prevent the spread of invasives. Every dollar we’ve put into it fights all of these things. We don’t want any of these getting into our lakes, not only for all the people that use our lake, but also for all the lakes around us. If we get it here we become a vector for all the other lakes. So we believe that fighting invasives is worth our effort. We would like to see the laws change so that all of us who are in this fight can do a better job."
In particular, Hector noted that there are no regulations that require a boat to be decontaminated after exiting an infested lake, and said he would like to see more robust restrictions to safeguard waters not yet infested.
Treatment options
Blue Water Science and the DNR were still compiling their information last week, and McComas said the next step would be to compare notes and talk with the lake association about what steps it might like to take next.
"It could an eradication effort. It could be something else," he said.
Jurek noted that it was up to the lake association to decide what additional steps it might like to take as far as contracting with a third party like Blue Water Science to do additional searching or treatment. The DNR also has a pilot program to treat zebra mussel infestations, but that program is still developing.
"Most of the time that a lake is infested with (aquatic invasive species), you can’t eradicate that species," she said. "You can manage plants, for example, in a lake once a lake becomes infested, but there hasn’t been a successful zebra mussel treatment in Minnesota as of today. There is also an infested water body upstream, Lake John, so they also have that flow coming into Lake Sylvia as well. That makes it a little more challenging."
One female zebra mussel can produce 100,000 to 500,000 eggs per year. The mussels are quite small, ranging in size between a quarter-inch and an inch-and-a-half, but like to attach to hard surfaces like docks and boat lifts. In large numbers they can impair recreation by an accumulation of their sharp shells, forcing swimmers to wear water shoes. They can also attach to boats and motors.
While zebra mussels filter tiny particles out of the water – making it clearer but removing nourishment for other aquatic species and potentially disrupting the food chain – Jurek said last July that it is difficult to forecast what impact the mussels will have in any given lake.
"Each lake responds differently to zebra mussels, so it’s really hard to predict what their densities will look like and how it will affect the fish population," she said.
Last week, she added that Sylvia has not lost its recreational value.
"You can still fish, swim and recreate in the lake. It’s just that if you visit the lake you need to be more careful about draining standing water, pulling your drain plug, and being conscientious about removing all invasive species from your boat before entering a different water body," she said. "People just need to be more aware."
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