Lake Pend Oreille’s noxious weed problem has worsened over the past six years, as blooms of invasive Butomus umbellatus, or flowering rush, have joined Eurasian milfoil to clog area waterways. The U.S. Army Corps of Engineers enacted targeted herbicide treatments at portions of waterways to control most of the flowering rush.
According to the Corps, the densely packed flowering rush can “degrade water quality (including impacts on irrigation and potable water), decrease aquatic biodiversity, negatively impact fish and wildlife habitat (including bull trout), harbor swimmers itch and interfere with shoreline activities.”
Herbicides are used both in conjunction with — and as an alternative to — physical control methods; however, they have the potential to harm native plant species growing in or near the application sites. Additionally, the leftover decomposing plant matter draws oxygen from the water, which can harm nearby fish.
There were no fishing or swimming restrictions in place at the treatment sites, however, locals were advised to wait three days before drinking the water or irrigating their landscapes, and five days before watering their crops, according to the Corps’ treatment notice.
Lake Pend Oreille in the northern Idaho Panhandle is the largest lake in the U.S. state of Idaho and the 38th-largest lake by area in the United States.