There will be no fishing or swimming allowed Tuesday through Thursday at Lone Star Lake.
Douglas County workers will be applying a herbicide called Aquathol K to kill a troublesome vegetation growing in some parts of the lake.
The vegetation, called curly leaf pondweed, has been prolific this spring, especially along banks, said Keith Browning, the county's public works director.
The weed, which is submerged, interferes with some recreational activities and often clogs boat propellers.
Aquathol K is approved for aquatic use by the Environmental Protection Agency. The county also consulted Kansas Department of Wildlife and Parks about its use. A state fisheries biologist will be present when the herbicide is applied, Browning said.
The area to be treated is in the southwestern arm of the lake, but swimming and fishing on the entire lake will be banned for three days.