Growing problem
On the north end of Newman Lake, the water is so thick with noxious Eurasian milfoil you could part it with a comb.
Long, fernlike tendrils trail upward from depths 12 feet and lower, casting a dark eclipse on the lake bottom where other plants starve for light. An aquatic rat’s nest is forming near the surface making the area unpleasant, if not un-navigable, for swimmers or boats.
Eurasian milfoil plagues many Eastern Washington lakes, biologists say, including in Newman, where 30 acres are being treated with herbicide. Nothing seems able to deliver a knockout punch to the noxious weed.
“We’re four years in,” said Marianne Barrentine, Spokane County’s Newman Lake engineer. “We treated 20 acres the first year, 10 the second and then last year it just took off to 60 acres.”
Shallow lakes like Newman and Liberty Lake, 10 miles to the south, can be clobbered by Eurasian milfoil because the lakebed is ripe for growing almost out to its center. At their deepest, the lakes measure about 30 feet. Eurasian milfoil can take over areas as deep as 20 feet. BiJay Adams, protection manager for Liberty Lake, said the problem is here to stay.
“It’s a continuous struggle,” Adams said. “We first found it in Liberty Lake in 1995 and started using herbicide in 1998. Before that we were successful with hand pulling. Now there are lots of plants scattered across the shoreline and we can’t hand-harvest the whole shoreline.”
Milfoil is a fast spreading water plant that can quickly form a weedy blanket on the surface of lakes and ponds. That blanket can entangle swimmers, foul boat propellers and drive away ducks and geese. Left alone, the weed also can grow thick enough to clog irrigation intakes and even block conduits.
The weed also can be bad for fish, said Ken Merrill, biologist with the Washington Ecology Department. Thick mats of milfoil give fish little living room in areas as shallow as 20 feet or less. It’s appetite for oxygen can leave little for fish to breathe.
Milfoil can grow so thick it leaves no channels for fish to swim through. In some places where the weed has taken over, biologists are working to cut channels for fish travel into the invasive mat, Merrill said.
“I don’t think we’re going to eradicate milfoil,” Merrill said. “It’s another weed that’s going to be around and going to have to be dealt with on a continual basis. Hopefully, we’ll find a biological way to control it.”
Sacheen and Loon lakes also were treated with herbicide this year, Merrill said. For now, poisoning or hand pulling the weeds seems like the only viable options. However biologists in other states are now experimenting with aquatic beetles as a means of controlling Eurasian milfoil.
The beetle, known at the “milfoil weevil” is a native insect that makes meals and nests out of non-Eurasian milfoils that grow naturally in American lakes and pose little problem. But the native bug seems to prefer the foreign milfoil, Merrill said.
Female weevils deposit two eggs a day into the stem of the milfoil plant. The larvae then mine the stem’s insides to stay alive, killing the milfoil. Researches at Appalachian State University in Boone, N.C., found that a female milfoil weevil might produce more than 500 offspring in her life.
Washington and Idaho are among 15 states where the weevils are known to exist, but there’s more Eurasian milfoil than biologists believe the weevils can handle. Boosting the weevils’ population might be one way to chew down the milfoil problem, Merrill said, but nothing’s been done yet to increase the beetles’ numbers.
On Liberty Lake, Adams and others have been scuba diving around the shoreline pulling the weeds by hand. It’s a tedious job. Millfoil roots splay like fingers deep into the lake sediment. Pulling the weeds by hand means digging through the silt so the weed’s gangly anchor can be shaken free.
If any piece of the plant is broken off in the pulling, then the exercise is all for naught. A small segment of milfoil can settle to a lake bottom and start a new plant. Two years after being introduced, Eurasian milfoil can take over an entire lake, according to the Washington State Department of Ecology. Biologists blame fragments hitchhiking on boat propellers for spreading the weed in Washington lakes beginning in 1965. Outbreaks in Western Washington hug the Interstate 5 corridor.
Roughly $1 million a year is spent on fighting milfoil. Much of that goes to herbicides like 2,4-Dichlorophenoxyacetic acid, which is sprayed in Newman and Liberty lakes. The herbicide, found in more than 1,000 products, has drawn criticism recently in the Idaho Panhandle where it’s being used for the first time to battle Eurasian milfoil there.
At higher concentrations, 2,4-D has been linked with joint stiffness, nausea and even liver and kidney problems in people working closely with the herbicide, according to the Environmental Protection Agency. The federal agency has not studied 2,4-D for human cancer risk. The agency notes that private studies have suggested an increase in tumor formation, though research failed to pinpoint 2,4-D as the specific cause.
However at the low concentrations used for treating Eurasian milfoil, 2,4-D is not considered harmful to humans or animals. At low doses, the herbicide seems to pass through mammals fairly quickly. Fish show no sign of the herbicide within three to seven days after a spray according to the National Library of Medicine.
On Newman Lake this year, biologists placed a three-day warning on irrigating or drinking the water within a quarter mile of a spray, Barrentine said. Swimming in those areas was off limits for one day.