$4 million funds Eurasian watermilfoil clean-up in Idaho's prize lakes

by Mary Ann Reese

When the Idaho Legislature and former Gov. Dirk Kempthorne in April approved $4 million in grants to fund a two-year battle with Eurasian watermilfoil (EWM) in Idaho's waters, it was a significant victory for the Gem State's invasive species warriors.

   Mat of Eurasian watermilfoil on Lake
   Pend Oreille, above, covers 20 acres.
   At top UI graduate student Karen Laitala
   helps prepare bottom barier to
   smother yhe weed at south of
   Coeur d'Alene Lake.
   Dave Lamb samples
   EWM with a weed rake.
   Photo Dave Lamb and
   Rep. Eric Anderson

"I celebrate them," said Idaho State Department of Agriculture (ISDA) Director Pat Takasugi, whose department set May 15 deadlines for grant money applications. They "made it clear they want to get a handle on this problem immediately."

Possibly brought to Idaho via recreational boaters from infested states, mere fragments of the weed can take root. In time, it can form ugly brown mats on the water's surface, easily entangling swimmers and boat propellers. It also threatens fish habitat by depleting water of its oxygen.

"With the $4 million, we can get a rapid response to begin eliminating this stuff," believes Tom Kerr, Valley County commissioner, who represents Idaho's counties on the governor's Invasive Species Council. Payette Lake has removed 100,000 pounds of the weed from its waters over four years. Last year, infestations dwindled to several thousand pounds removed. But without vigilance, it will return.

Surveying Idaho lakes

UI's Tim Prather, on Idaho's EWM Task Force, helped organize a survey of Idaho lakes that documented 4,000 to 7,000 acres infested and another 250,000 acres as susceptible to invasion.

Worst hit are Lake Pend Oreille, Hayden Lake, and southern reaches of Coeur d'Alene Lake. It's also in Ada County and other southern Idaho ponds. Prompting the legislature to act were the task force's map, plus photos and presentations by legislators including Rep. Eric Anderson.

"Both the House and Senate were extremely receptive once they had the facts," says Anderson, who confesses he was "very noisy" about the problem.

The $4 million was based on ISDA Matt Voile's estimates that it takes $1,000 to clean up one acre of weeds.

Prather works with College of Natural Resources' Cort Anderson to understand the weed's genetics, and is studying the effectiveness of three methods to rid lakes of this plague—herbicides, hand pulling by divers working with dredges, and a bottom barrier Prather had a hand in developing.

The 10 x 10-foot black barrier smothers Eurasian watermilfoil and is especially effective in shallow shorelines and around docks. Whether it will come back once the barrier is gone is one study Prather is conducting with UI graduate student Karen Laitala.

Hybrid a new threat? Native to Europe, Asia, and northern Africa, Eurasian watermilfoil (Myriophyllum spicatum) has been in the U.S. since the late 1800s. It was first documented in Idaho in the 1990s. It looks similar to a native harmless Northern watermilfoil (Myriophyllum sibiricum). Cort Anderson, Prather, and others are running DNA tests and watching a hybrid of the two found recently in northern Idaho, worried it may turn out to be yet another problem.

"One good thing is that EWM is not believed to produce viable seeds if you catch it before it reaches the surface," says Dave Lamb, task force chair, hired by the Coeur d'Alene Tribe to solve its EWM problems. "So if you get it all, it should be gone."

Contact Prather at tprather@uidaho.edu.

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