Decked out in diver’s gear, Glenn Edwards submerged for a search-and-destroy mission Friday. His target: Eurasian milfoil.
The invasive aquatic weed has gained a toehold in the St. Joe River, a tributary of Lake Coeur d’Alene. To keep the milfoil from invading new territory downstream, the Coeur d’Alene Tribe hired divers to suction it off the river bottom.
“We don’t want it spreading northward into the lake,” said Dave Lamb, the tribe’s lake ecologist.
Earlier this month, the tribe sprayed 100 acres of southern Lake Coeur d’Alene with an aquatic herbicide, 2, 4-D. The herbicide effectively combats milfoil where it forms thick mats of floating vegetation. But it’s less practical for fighting smaller pockets of the weed in flowing waters.
That’s where the divers come in. They’ll scout the river bottom, and part of the St. Maries River, canvassing the area twice over a 40-day period.
“We’re hoping to knock it back by 90 percent,” Lamb said.
Eurasion milfoil is the bane of boaters, swimmers and wildlife. Dense colonies of the non-native weed can snare boat propellers and entangle swimmers. Milfoil’s rapid growth allows it to crowd out beneficial aquatic plants that provide wildlife habitat.
An inch of stem can regenerate an entire milfoil grove.
“Every little fragment can make a new plant,” Lamb said. “The first year, you get a single stem about 3 feet tall. By the second year, you have multiple stems.”
On Friday, Edwards worked the river bottom, while colleague Mike Kinzer steered a pontoon boat. The two men work for Aquatic Consulting and Evaluation in Spirit Lake, Idaho. The firm specializes in eradicating invasive aquatic plants.
The work is labor intensive. Edwards identified Eurasian milfoil by its intense green, hair-like fronds, using the dredge to suck the stringy plants into a mesh basket on the boat.
“You try to get the roots, too,” he said.
When the basket filled up, Kinzer raked the masses of vegetation into plastic bins. The milfoil is dumped onshore, where it dries up and dies.
The tribe received a $143,000 grant from the Idaho Department of Agriculture this year, which pays for the majority of the tribe’s milfoil control efforts. A four-year, focused effort on milfoil is showing results, Lamb said.
Big mats of the weed are disappearing in the southern end of Lake Coeur d’Alene, he said. Controlling milfoil in the lake’s southern territory is critical, because the wind blows the water in a northerly direction.
Next year, Lamb also hopes to employ a weevil in the tribe’s milfoil fight. In Lake Pend Oreille, where using herbicides has been controversial, the Tri-State Water Quality Council is coordinating a $195,000 effort to use weevils as a biological control.
The weevils, which bore into the plants’ stems, are found on Northern milfoil, a strain native to local lakes. The weevils will be gathered, propagated and re-released in greater numbers, said Diane Williams, the council’s executive director.
“The weevils seem to prefer the Eurasian milfoil,” she said. “We already have them in our watershed, but not in large enough numbers to make a difference.”
The first weevil release into Lake Pend Oreille is scheduled for later this summer. As weevils become available, Lamb wants to release them into Harrison Slough, which is part of the chain of lakes feeding into Lake Coeur d’Alene. The slough is a popular fishing spot, and anglers have opposed using herbicides to treat milfoil there, Lamb said.