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Zebra mussels continue explosive growth in Green Lake

Zebra mussels cover rocks and hard substrate throughout Green Lake, and the presence of veligers in the water indicate that they are poised for a second year of growth. These mussels were on a rock pulled from the waters of the Saulsbury Beach access in Spicer. (TOM CHERVENY | TRIBUNE) 1 / 2
Rob Miller and Amanda Sabrowsky ready their new boat for its maiden voyage on Green Lake on June 11 in Spicer. (TOM CHERVENY | TRIBUNE) 2 / 2

SPICER — Zebra mussels are likely to continue their explosive growth in Green Lake this summer, but it remains impossible to know what their presence in the lake will be like in the long-term.

“I want to emphasize. It is very unpredictable for each water body,’’ said Tim Plude, invasive species specialist with the Minnesota Department of Natural Resources. Plude spoke about the zebra mussel population as well as efforts to guard against the introduction of starry stonewort to the Green Lake Property Owners Association at its annual meeting on June 11.

Zebra mussels were first confirmed in the lake in July 2104, and last year their numbers proliferated wildly. The same appears likely this year. DNR staff recently pulled tows in the lake to catch the tiny, often microscopic-sized veligers that grow to become adult mussels.

They found them. “So that means they are reproducing already this spring,’’ said Plude.

And of course, the small mussels are already visibly covering rocks and hard substrate all over the lake.

It is typical for zebra mussel numbers to grow rapidly once they’ve become established in a lake. They can grow in numbers to the point that they eat up their algae food supply and crash. They can level off and maintain a certain population density on rocks, docks and the hard substrate on which they attach.

In Lake Carlos of Douglas County, zebra mussel numbers started decreasing four years after their introduction, Plude said.

The large numbers that follow a new infestation don’t by themselves tell researchers what lies ahead. Every lake responds differently. The availability of calcium in the water, the food supply, and the amount of hard surface substrate are all factors that will determine their long-term population.

Green Lake residents at the meeting reported that they are experiencing the negative consequences of the infestation. The small mussels are getting into irrigation pumps, and people are cutting their hands and feet on the sharp shells.

Plude cautioned against spreading panic about their presence. With no effective means to control them, spreading a message of fear or panic is not going to produce a better management outcome, he noted.

Without a doubt, their presence in the lake will have consequences for the aquatic plants and fish. Zebra mussels are stealing food from native organisms, he pointed out.

“They are very harsh on a lake’s eco-system,’’ said Plude. “I want to stress we don’t know exactly what’s going to happen with Green Lake. In the future we want to track and make sure we are keeping on eye on it.’’

Efforts to monitor watercraft using the lake will continue as well. Three boat decontamination units will operate in the county this summer, according to Evan Freeman, inspection supervisor with the DNR. He is currently seeking staff for the third unit added to the arsenal.

The microscopic veligers pose the greatest threat for contaminating other lakes. They can be transported in bait buckets, live wells, or boat equipment, Plude pointed out. In response to questions, he said there is only a “very, very low chance’ that they could be spread to other lakes by birds.

Freeman said inspections and decontamination can be very effective. In response to questions, he said that the operating temperatures of Inboard/Outboard engines effectively “nuke’’ the zebra mussel veligers while running. There are concerns about the initial intake of water when the units are shut off, he added.

Tom Cherveny

Tom Cherveny is a regional and outdoor reporter with the West Central Tribune in Willmar, MN.

(320) 214-4335
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