Surface Water Management Division

Lake Management Program

Lake Shoecraft Milfoil Control Project

Eurasian watermilfoil is an aggressive, non-native aquatic plant that invaded Lake Shoecraft. Milfoil crowds out native plants, forms dense mats, and produces long tendrils that entangle fishing lines, boat motors, and swimmers. It spreads easily to other lakes from small fragments left on a boat motor or trailer.
Eurasian watermilfoil likely spread into Lake Shoecraft from nearby Lake Goodwin in the mid-1990s. The plant grew rapidly in the north and south ends of the lake. By 1999, milfoil covered about 20 acres in Lake Shoecraft. Snohomish County SWM and local citizens worked together to develop a plan to control the milfoil. The main strategy was to apply a herbicide behind temporary fabric containment barriers stretched across the north and south ends of the lake. The adjacent map shows the milfoil beds in red as well as the location of the containment barriers.
During the summer of 2000, SWM hired a contractor to assemble and install the containment barriers. The barriers came in panels 50 feet long by 20 feet deep, which were connected to adjacent panels with pins. The barriers contained flotation at the top and a heavy chain at the bottom.
Once installed, the fabric panels formed continuous containment barriers stretching from shore to shore and from the lake surface to the bottom. The purpose of the barriers was to hold the herbicide in the target zones and keep it from spreading throughout the lake.
Seen from the air, the containment barrier at the south end of the lake stretched almost one-half mile in length. The north barrier was 900 feet long. The barriers remained in place from the end of June 2000 until mid-September 2000.
Every two weeks, the contractor applied the herbicide Sonar® to the target areas behind the barriers. Sonar is a slow acting herbicide that acts on a pigment found only in plants. There were no restrictions for boating, swimming, or even drinking the water.

Results

The project worked. The containment barriers held the herbicide in the target areas, and the herbicide killed the milfoil plants. Twice-yearly diving surveys since 2000 have not found any milfoil growing in Lake Shoecraft.

This project and the on-going milfoil control work in Lake Goodwin is funded by Snohomish County SWM, citizens living around Lake Shoecraft and Lake Goodwin, and a grant from Washington State Department of Ecology.

Contact

Gene Williams, Senior Planner, 425-388-3464 extension 4563

Marisa Burghdoff, Water Quality Analyst, 425-388-3464

extension 4639