Zebra mussels, still not found in southwest Minnesota, explode in Iowa Great Lakes

SPIRIT LAKE, Iowa -- When the Minnesota Department of Natural Resources updated its infested waters list earlier this month, counties in southwest Minnesota remained clear of one of the most damaging aquatic invasive species there is -- zebra mus...

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Zebra mussels cover boat hoists removed from East Okoboji Lake in this image captured Tuesday. (Mike Hawkins/Iowa Department of Natural Resources)

SPIRIT LAKE, Iowa - When the Minnesota Department of Natural Resources updated its infested waters list earlier this month, counties in southwest Minnesota remained clear of one of the most damaging aquatic invasive species there is - zebra mussels.

The small freshwater mussel has infested 121 Minnesota water bodies, including 26 this year alone. While that number represents less than 2 percent of Minnesota’s more than 11,000 lakes, the preference would be that this threat didn’t exist.

Neighbors to the south in the Iowa Great Lakes are well aware of the problems caused by the sharp-sided mussels, which attach to everything from rocks and boat lifts to lost water goggles and ladders on water slides.

Mike Hawkins, fisheries management biologist with the Iowa Department of Natural Resources at Spirit Lake, said a single live veliger, or juvenile zebra mussel, was discovered in Upper Gar Lake - just south of East Okoboji Lake - in 2012. By that fall, two dead adult zebra mussels were found on boat hoists in East Okoboji Lake.

“In all of the looking we did, we only found those three,” Hawkins said. “By 2014, numbers on East Okoboji exploded to pretty high levels. In 2015, every structure I looked at on West Okoboji had zebra mussels on it.”


When boat and personal watercraft lifts were pulled from the lakes this fall, Hawkins said it was clear the zebra mussel population had continued to explode.

“Pretty much every hard structure under the water had some zebra mussels on it,” he said.

Based on research of zebra mussels in other water bodies, Hawkins anticipates the population of zebra mussels will peak in West Okoboji Lake in a couple of years.

Here to stay Once a lake is infested with zebra mussels, there is very little that can be done to control them. Hawkins said it’s kind of a common theme with invasive species in general. Consider the common carp, an invasive species introduced to Midwest waters in the 1880s as a game fish, and what that fish has done to lake ecosystems. Nowadays, the zebra mussel is one of the most threatening invasive species, but it isn’t the only one. Bighead and silver carp, Eurasian watermilfoil and starry stonewort are among just a few species of invasive aquatic animals and plants on the move.

Dennis Heimdal, environmental lab specialist at Iowa Lakeside Laboratory in Spirit Lake, said zebra mussels can be detrimental to a lake’s ecosystem and create a danger to swimmers because of their sharp, pointed shells.

“As of right now, there really isn’t a way to kill off the zebra mussels in a large lake,” he said. There is a bio-based product, Zequanox, that uses natural bacteria to attack zebra mussels, but its 2014 use in Minnesota’s Christmas Lake, in Shorewood and Chanhassen, proved unsuccessful.

With no way to get rid of the invasive species, Heimdal said agencies are learning how to deal with them. For instance, utilities pulling water from East and West Okoboji lakes to supply their communities with drinking water have had to add copper to their intake pipes to stop zebra mussels from clogging up the system.

Prevention through education While agencies learn to live with zebra mussels, Hawkins said the state of Iowa, like Minnesota, is still very much in education and prevention mode. They don’t want to see the spread of zebra mussels and, thus, they are doing what they can.


“What we’ve focused on and what we continue to focus on is the prevention of the spread,” Hawkins said. “We’ve become a very mobile society, and that is reflected even with boat traffic and moving boats and equipment from lake to lake - boat hoists, jet-ski hoists and docks. There is … an emerging thought that those might be a more common vector or mode for these (zebra mussels) getting from lake to lake.”

Still, Iowa is targeting money at education and outreach. It isn’t quite to the scale of what Minnesota has done, but Hawkins said the state is trying. A message of “Clean. Drain. Dry.” is carried on billboards and advertising campaigns, and delivered personally at boat ramps and boat inspection sites throughout the Iowa Great Lakes.

In 2015, Hawkins said between 14,000 and 15,000 personal contacts were made with boaters and others visiting any of the Iowa Great Lakes.

“As important as talking about bringing things in, we’re also focusing now on letting people know that once they are in infested waters, they can be transporting (zebra mussels) to other water bodies,” Hawkins said.

The messaging is working.

“We’re seeing very large increases in awareness - not just zebra mussels, but other (invasive species) as well,” Hawkins said.

High stakes People who continue to take a gamble by not following the rules - pulling drain plugs before leaving a lake, powerwashing watercraft before entering a different lake and removing any plants from boat motors and trailers before transport - leave lakes at high risk for being the next infested water body to be added to the list.

Hawkins said there has been a lot of concern in the Iowa Great Lakes about the economic impact zebra mussels could have on the local economy.


“There are a lot of businesses and entities that really survive or rely on tourism,” he said. “Homeowners were worried with their home values.”

Three years after the first veliger was discovered, and two consecutive years of population explosion for zebra mussels later, Hawkins said there hasn’t been much research on the economic impact.

“In general, we can say there is probably little to no impact in terms of recreation,” he said. People just need to change their habits, he added. If they plan to swim in a lake where zebra mussels are present, they should wear foot protection to avoid being cut or scraped by the invasive mussels.

“I sure hope people are thinking about (the impact of spreading invasive species),” Hawkins said. “There are really simple things people can do not to bring them back with them - clean, drain and dry. Pull your plugs out of your boat - that’s the law in both states. Get all of the plants off.”

Hawkins said contacts will continue to be made with boaters in 2017, and the message about zebra mussels and other aquatic invasive species will continue to be spread.

In Nobles County, money has again been issued by the state in 2017 to target invasive species education and prevention

Julie Buntjer became editor of The Globe in July 2021, after working as a beat reporter at the Worthington newspaper since December 2003. She has a bachelor's degree in agriculture journalism from South Dakota State University.
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