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'Pondweed Has Got A Hold In This Area': Invasive Plant Had Tricky Grip On Iowa Lake This Year

Courtesy of Iowa DNR
When curly-leaf pondweed starts to grow in fall, it produces oxygen underwater and creates habitat for fish. As the plant dies back in summer, it takes that oxygen out of the water and can pose a threat to those fish.

The Iowa Department of Natural Resources has wrapped up this year’s efforts to treat an invasive plant in the Iowa Great Lakes region. Efforts mostly worked against the plant that grew a little differently than past years, said a biologist.
Thick, invasive curly-leaf pondweed can create habitat for fish when it grows in the water, but it also can hinder boater access and even later cause algae blooms when it dies back in summer. Iowa uses two methods to treat it: An aquatic herbicide and a boat that cuts and harvests the weeds. The DNR and the locals involved treated a little less than the 85 acres they planned to treat on East Okoboji Lake.  

It's a battle unfortunately that can only be fought. It can't be won.<br>-Terry Wilts, East Okoboji Lakes Improvement Corporation

The plant didn’t reach above the surface in all of the places where a treatment was used, probably because of cooler temperatures this spring, said Mike Hawkins, a fisheries biologist with the Iowa DNR. Hawkins said that made the mechanical harvesting process difficult.

“When it’s just below the surface, it gets hard to see, it’s hard to navigate out there,” Hawkins said. “It’s analogous to mowing the grass when you can’t see where you’ve been.” 

The mechanical harvesting process generally takes a little over two weeks, Hawkins said. Contractors remove the plant material and bring it to a composting site. The harvester couldn't get all the acres the DNR and locals had hoped because there were "issues with some of the equipment," Hawkins said, and there seemed to be less curly-leaf pondweed in some of the areas where contractors planned to use the harvester. 

The herbicide treatment took one day and knocked back around 60 acres of pondweed, Hawkins said. He said there were some difficult spots where the plant continued to grow, but, "by and large, we had a successful treatment."

Because it was hard to see, the pondweed deceived some boaters who recreate on East Okoboji Lake, who at first thought it was a lucky spring for them. Terry Wilts, who lives on the lake and is the secretary for the East Okoboji Lakes Improvement Corporation which helps in the efforts to treat the pondweed, said he was surprised when he first took his boat out on the lake in spring.

“The weeds grabbed ahold of my boat and stopped it right in its tracks,” Wilts said.

Wilts estimates he has put in over 40 hours on his boat so far this year, “even through the nastiest time of the weeds.” He said he's not going to let the pondweed stop him from enjoying the lake.

“It’s a battle unfortunately that can only be fought. It can’t be won," Wilts said. "Pondweed has got a hold in this area.”

Curly-leaf pondweed has already died back on East Okoboji Lake. Hawkins said he is concerned the breakdown of the plant could fuel algae blooms on the water.

“The worst thing that can happen when something like that happens is we would have a summer kill, a fish kill, that so far hasn’t happened,” Hawkins said. “We’ve been fortunate that that hasn’t happened.”

In July 2015, the plant died back in north-central Iowa’s Crystal Lake, where it lowered oxygen levels and caused a large fish kill.

Hawkins said the plant seems to grow differently every year, making it tough for scientists and locals to predict what’s next.

The state used $50,000 in funding through the state’s Marine Fuel Tax Fund and donations from local government officials, local business owners, water utilities, lakeshore homeowners and groups like the East Okoboji Lakes Improvement Corporation to treat the pondweed.