The Idaho State Department of Agriculture set its sights on ridding Lake Pend Oreille of an invasive weed earlier this week.

Using herbicides and divers, the ISDA is targeting the Eurasian watermilfoil, an invasive weed that can quickly spread. Sydney Kennedy, ISDA spokesperson, said in an email that the weed can create thick plant beds that kill native plants, reducing fish habitat and make swimming and boating difficult. 

Only selected locations in Lake Pend Oreille were targeted, with the largest areas of herbicide use taking place in Bottle Bay, Ellisport Bay and off the north end of the Long Bridge by Dog Beach. Smaller applications were done around those areas and in Garfield Bay. 

The herbicide used by the ISDA, ProcellaCOR, comes with no recreational restrictions and the water in the lake remains safe for swimming and other recreational activities. 

ProcellaCOR is a common herbicide used in the management of freshwater vegetation, like the Eurasian watermilfoil. The ISDA says it measures the amount of invasive weed on a yearly basis, and those surveys determine if herbicide use is warranted. 

“When herbicide is used, applications are performed by professional contracted applicators with experience,” Kennedy said in the email. “For this treatment, the herbicide is applied below the surface at the target plant height to be as precise as possible.” 

According to the U.S. Environmental Protections Agency’s report on ProcellaCOR, the only risk posed to humans is mild eye irritation, but a person would need direct contact with the herbicide to get any effects. 

Kennedy said the ISDA does not plan on carrying out any more treatments in Lake Pend Orielle this year but noted other treatments from agencies and landowners might occur. 

"The approach of using survey results to guide carefully targeted herbicide treatments has proven effective in reducing the spread of Eurasian watermilfoil in waterbodies across the state including Lake Pend Oreille,” Kennedy said.