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Fremont County, Idaho

Closeup of Eurasian watermilfoil

The Eurasian watermilfoil leaf generally has 12 or more leaflet pairs, not to be confused with the native plant, Northern watermilfoil, that has under 12 or more leaflet pairs.

Boat Washes

 

Boat Washes on Henrys Lake Help Prevent Spread of Eurasian Watermilfoil

Eurasian watermilfoil is a highly aggressive aquatic plant that can form dense mats which congest waterways and crowd out native aquatic plants. It has no natural enemies to control it in Idaho. While this thick growth may impair recreation uses of a waterway including boating swimming and fishing; dense growth can lead to deteriorating water quality in infested waterways, thereby altering and degrading the habitat of native fish and wildlife. Eurasian watermilfoil can cost lake users millions of dollars a year to manage.

Fremont County has recently acquired grant money to help prevent Eurasian watermilfoil from entering its waterways. This grant has made it possible for Fremont County to conduct boat washes and inspections this year on Henrys Lake. Boat washes will be mandatory for boats that are suspected to have a high risk of transporting this plant, especially for boats which have been previously on bodies of water that are known to be infected with Eurasian watermilfoil.

Eurasian watermilfoil is readily spread by plant fragments that may be carried inadvertently by wind and water currents or dispersed by boats, motors, trailers, live wells, bait buckets or fishing gear. These fragments can stay alive for weeks if they remain wet. Many conditions make Henrys Lake a perfect environment for this plant to grow, including its depth, water temperature, and rich soil. The number of boats on the lake each year also highly increases the chances of the plant being transported to Henrys from already infected waters. Once infected with Eurasian watermilfoil, the fish habitat in the lake could be destroyed in 5-7 years if no management practices are done.

Everyone engaged in activities on waterways should be aware of the potential of spreading this invader and know how to identify it. Eurasian watermilfoil has a feather-like appearance, and the topmost leaves and stems may be reddish-brown or pink. It has twelve or more pairs of leaflets, while Northern watermilfoil (which is naturally found in Henrys Lake) has less than twelve pairs of leaflets. Mature leaves are usually arranged in whorls of four around the stem.

The Eurasian watermilfoil leaf generally has 12 or more leaflet pairs, not to be confused with the native plant, Northern watermilfoil, that has less than 12 leaflet pairs.

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