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Environment

DNR Will Tackle Iowa Great Lakes-Area Invasive Weed

curlyleaf_pondweed_2019.jpg
Courtesy of Iowa DNR
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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 is working to control an invasive aquatic plant and improve access for boaters in the Iowa Great Lakes region.
Once the ice melts on the lakes, the Iowa DNR plans to tackle 85 acres of curly-leaf pondweed in the East Okoboji Lake area using an aquatic herbicide and a boat that cuts and harvests the weeds.

Curly-leaf pondweed is native to Eurasia, but has become widespread throughout the Iowa Great Lakes. When it 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.

Though large fish kills related to curly-leaf pondweed have not been seen in the Iowa Great Lakes, in July 2015 in north-central Iowa's Crystal Lake, the plant died back and lowered oxygen levels, which caused a big fish kill.

In the Okoboji area, “that is a fear,” said Mike Hawkins, a fisheries biologist with the Iowa DNR.

The agency is using $50,000 in funding through the state’s Marine Fuel Tax Fund and donations from lakeshore homeowners to treat the weed.

Hawkins said there’s no way to destroy curly-leaf pondweed completely, but they’ll clear as much as they can to improve lake access.

“It will bring relief to lakeshore homeowners, boaters trying to get around in those areas, folks that are trying to use the public boat ramps in that area and get to other parts of the lake,” Hawkins said.

Though curly-leaf pondweed can grow in dense amonts, forming thick clumps and not allowing other varieties of plants to grow through, the weed does have some benefits.

“We’ve documented an increase in water quality and clarity in East Okoboji Lake as well as an increase in number of panfish species growing there,” Hawkins said.

In 2018, the DNR treated about 60 acres in the Iowa Great Lakes. There are about 700 acres across the lakes area where the plant grows above the surface and restricts boater access.