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Late ice delays curlyleaf pondweed growth in Iowa Great Lakes

SPIRIT LAKE - The record breaking late ice on the Iowa Great Lakes delayed curlyleaf pondweed growth in the Iowa Great Lakes, but it will top out in portions of East Okoboji Lake and other lakes this week.

“The plant is only a foot or so below the water’s surface in most locations and looks to be growing in the same areas where we saw it last year,” said Mike Hawkins, fisheries biologist with the Iowa Department of Natural Resources (DNR). “We had hoped that the long winter would knock it back, but it looks like it just delayed its growth.”

Curlyleaf pondweed is a non-native plant first discovered in the Iowa Great Lakes more than 70 years ago. This fall germinating plant does best with late fall ice-up and low early snow cover. The past few years have provided optimal growing conditions in lakes around the region.

The management plan developed by a community working group last fall is being implemented.

The first step was to treat two 10-acre areas in the north bay of East Okoboji Lake and Lower Gar Lake with an herbicide on May 9.

“We’re monitoring these treatments, but early indications are that they were successful. We’re seeing very few plants in these areas,” Hawkins said.

The second step includes expanding mechanical plant removal from 20 acres last year to 40 acres this spring. Mechanical harvesting efforts are just getting started.

These treatments are strategically placed to create lanes for boat traffic and ease access at boat ramps and from private docks. Iowa Great Lakes homeowners and lake users have expressed concern about plants washing to shore and piling up around docks and hoists. 

“A lot of loose, curlyleaf pondweed was floating on the surface right after ice out this year. This was probably caused by the plant being caught in the shifting ice and being pulled up,” said Hawkins. ”We have witnessed a lot of plants being cut by boat and barge propellers. There was concern that clippings from mechanical harvesting are to blame, but that material is removed from the lake when it is cut and composted at approved disposal sites.

“Eradication of the plant is not feasible. We need to work together as a community to help lessen some of the impacts with the few options we have.”

Private application of herbicides by homeowners in public water is strictly prohibited and can be dangerous if not done correctly. Lakeshore residents can remove plants around their dock and hoist by mechanical cutting, pulling or raking without a permit. Dispose aquatic plants on the adjacent property or haul them to a disposal site. Transportation of plants and zebra mussels is allowed by obtaining a free permit at the Iowa DNR’s Spirit Lake Fish Hatchery. 

The East Okoboji Lakes Improvement Corporation and the City of Orleans have been active partners in this project, providing funding and contracting services for the work. Additional funding has come from the Marine Fuel Tax fund used to improve and maintain boating access in Iowa.

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