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WATERLINE - March, 2011

Volunteer detects aquatic invader in Snohomish County

by Marisa Burghdoff, Snohomish County

An unwelcome visitor has been identified in Washington’s lakes, thanks to the vigilance of Billie Garber, a volunteer lake monitor for Snohomish County’s Lake Management Program. On a routine monitoring trip to Echo Lake, Billie noticed a new patch of plants by the public boat launch and submitted a sample of the suspicious plant for analysis. The plant was identified as Marsilea mutica — Australian water-clover — by Snohomish County staff. Its identity was later confirmed by Jenifer Parsons, an aquatic plant specialist with the Washington State Department of Ecology.
Marsilea mutica

The water-clovers are actually a type of water fern distinguished by their four-lobed leaves. Marsilea mutica is characterized by its two-tone leaves. The plant has an appealing appearance, but is an aggressive invader that spreads rapidly through rhizomes. This was clearly the case at Echo Lake where a 10-by-20-foot patch established itself in just a few months.

Although this plant has been problematic in the Southeast U.S. for a number of years, it is very new to the Northwest. In Washington, the plant had previously been found only in private ponds in Whatcom and Pacific Counties. The suspected method of introduction is through local sale as an aquarium plant and subsequent disposal at the boataquatic invader in Snohomish County launch. The plant will likely be added to the state quarantine list in 2011, which should help prevent future introductions. Ideally, control at Echo Lake will be achieved in the next year through bottom barriers or herbicide treatments before the plant becomes a problem there or has a chance to spread to other lakes.



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