Researchers say a noxious weed has clogged up more than 2,000 surface acres of Flathead Lake and warn that, if left unchecked, flowering rush could change the lake's ecology.

Peter Rice, at the University of Montana, and Virgil Dupuis, at Salish-Kootenai College, are working together to find ways to control the nonnative weed, which has already spread to the Clark Fork River and downstream to Lake Pend Oreille, in Idaho.

Rice notes that Flathead Lake has gone from one recorded infestation in 1964 to "uncountable" numbers 50 years later. If left unchecked, flowering rush could spread all the way to the Pacific Ocean, he said.

Montana, Idaho, Washington, Idaho and Oregon have declared flowering rush to be a noxious weed. Rice and Dupuis say certain herbicides can knock down the weed for a year and a half, but it usually comes back.

Noting that their funding is limited, the two researchers say different ways to apply herbicides have been tried over the past three years of study. One method cost $1,300 to $2,400 per acre.