Cerro Gordo supervisors approve plan to combat Eurasian watermilfoil in Clear Lake

MASON CITY — The Cerro Gordo County Board of Supervisors has approved signing a letter of support for the Iowa Department of Natural Resources efforts to eradicate Eurasian watermilfoil from Clear Lake with herbicide treatments.

Eurasian watermilfoil is a non-native submersed, rooted aquatic plant that is native to Europe and Asia that impacts an aquatic ecosystem by reducing the sunlight availability, which reduces native aquatic plant germination and diversity.

Eurasian watermilfoil was first identified in Clear Lake in the late fall of 2023, and aquatic vegetation surveys of the lake were conducted last year. Two large spot treatments were also completed last year to reduce the plant’s abundance. The initial treatment cost is estimated to be about $280,000, which will be covered by the DNR.

Supervisor Casey Callanan says additional treatments may be needed after the initial treatment during the 90-to-120 days required concentration period. “They have a deal right now where the DNR is going to spray in mid-to-late October, the entire lake, to see if that knocks down some of the vegetation. This is merely saying that the county in the event what they’re doing isn’t adequate, the county along with the other two entities Ventura and Clear Lake would pay for a second application.”

Those additional treatments would cost about $170,000, which would be covered through contributions by the cities of Clear Lake and Ventura as well as the county. Callanan says treatments in other bodies of water have been successful after only one round and a second round hasn’t been needed.   “The Association for the Preservation of Clear Lake is going to pay for the ongoing monitoring after the first application to see if the second one is necessary. They would still try to do that before the freeze in the fall in the event that it’s necessary.”

Along with the approving of the letter of support, the supervisors pledged $68,000 for additional treatments if necessary.

The Clear Lake City Council last week approved a similar financial commitment of up to $85,000.