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Controlling the milfoil

PLUMMER, Idaho – The Coeur d’Alene Tribe has management control on the south end of Coeur d’Alene Lake and it’s in these waters that Eurasian watermilfoil began appearing several years ago.

David Lamb was working for the tribe in their fisheries division when he first noticed a significant patch of milfoil in Chatcolet Lake which abuts Coeur d’Alene Lake. Lamb transferred to the Lake Management Department within the tribe in 2003 and since then has spent considerable amounts of time overseeing a program to control milfoil, and recently reported a significant reduction.

Eurasian milfoil is native to Asia and Europe, but was introduced to the United States many years ago. It has become a severe problem in waters throughout the country. When not controlled it can choke waterways and make recreational uses such as boating, swimming and fishing nearly impossible. It can also block water intake tubes, causing problems for irrigation or power generation. It sometimes forms thick mats of vegetation robbing the water of oxygen, trapping sedimentation, and creating mosquito breeding areas.

Lamb said milfoil spreads rapidly through fragmentation which frequently occurs when a boat passes through, chopping it up and spreading it throughout the lake where the pieces settle and begin growing again. It’s most likely spread from lake to lake throughout the country when boaters launch boats in different waters, not realizing that fragments of the plants are attached to their boat or motor. He feels it most likely came to Coeur d’Alene tribal waters in that way from a boat launching site upstream on the St. Joe River.

The State of Idaho began a funding program making roughly $4 million available annually to work on milfoil control. The Coeur d’Alene Tribe has applied for, and received, grants for the past four years. Those grants have averaged about $250,000 and the money has been used to hire contractors who utilize a variety of techniques to control milfoil.

Several lakes and the St. Joe River are interconnected in these tribal waters, further complicating the problem. Surveys must be conducted annually to locate concentrations of the plant.

“The water is not as clear on this end of the lake so we use divers when we’re doing surveys,” Lamb noted. “We pull divers behind a boat and they’re equipped with underwater communication so they can communicate with the boat and we log in points of milfoil locations and densities. It gives us good data so we can plan the next year’s treatment.

“We surveyed and treated Round Lake and managed to knock that back pretty well. Most work is now taking place on the south end of Coeur d’Alene Lake near the mouth of the St. Joe River.”

Work in that area is done using a herbicide treatment administered from an airboat. “The airboat is loaded with jugs of liquid 2,4-D with a product name of DMA4IVM. Liquids go into a tank on the boat and there’s water suction up into the tank where it’s mixed and then ejected off the bow of the boat in a series of hoses to a certain depth. It’s very specific to milfoil in a bed of other plants. The objective is to be selective and not affect native plants or wildlife or human uses of the lake.”

They have used a granular form in the past, but Lamb said it sometimes gets tied up in the organic matter on the bottom and isn’t released. “I’ve found this liquid form is very effective and also less expensive.

“We’ve seen a dramatic reduction in milfoil from what I first noticed and documented in 2004. There were some really dense patches of milfoil and those patches are pretty much gone.”

Eradication on the St. Joe River, upstream from the lake, is being done a little differently. A pontoon boat equipped with a dredge system is utilized.

“A diver is in the water, basically swimming along the shoreline,” Lamb said. “When he finds milfoil he’ll pull it up by the roots and suck it up into the pump which dumps it into a basket on the side of the boat so all the fragments are collected. The diver has a system with an air supply tube allowing him to remain underwater.”

Different contractors who have the necessary equipment are hired do the work, either herbicide application or diver/dredger, under Lamb’s direction.

The Coeur d’Alene Tribe recently signed a long term agreement with Avista Corp. which was approved by the Federal Energy Regulatory Commission. Avista owns the dam that controls water levels within the reservation. They will now provide $2 million annually in five subject areas, one of which is aquatic weed control. That fund will continue the milfoil control in the future.