Milfoil In Pend Oreille River Causes Concern

State and Bonner County officials may attack a new aquatic weed infestation with chemicals by the end of the month, and again in the spring.

University of Idaho researchers discovered Eurasian milfoil in the Pend Oreille River above Albeni Falls Dam last month, raising concerns it will eventually find its way into shallow areas of Lake Pend Oreille. By midweek it had spread to about 20 acres.

“We know the seriousness of the problem if we don’t do anything,” county Commissioner Dale Van Stone said.

The weed is thick in the river below the dam, as well as in many other Washington waters. It can stunt fish, suck oxygen from the water and hamper recreation.

“Typically in the Seattle area, there are three or four drownings a year that are attributed to milfoil” because it wraps around swimmers’ legs, said Terry McNabb of Resource Management Inc., a Seattlebased company the county has hired to help fight the infestation.

McNabb said he most likely would recommend a mild herbicide this fall to help the weed from spreading before it goes dormant. Then the more potent chemical 2,4-D would be used in late May or early June to kill the weeds.

It probably would take four or five years of treatments to reduce the weeds to manageable patches, McNabb said. It is nearly impossible to eradicate milfoil, especially in rivers where the current makes chemical treatment difficult.

The treatment could cost as much as $500 per acre this fall and $1,500 per acre in the spring, depending on which chemicals are used. Van Stone said the county and state agencies would share the cost.