Eurasian Water-Milfoil – Oneida County Aquatic Invasive Species Program

Identification: Long, underwater stems that branch. Delicate, feather-like leaves arranged in whorls of 3 – 5 around the stem. Usually 12 – 21 pairs of leaflets on a leaf. Eurasian water-milfoil often forms dense mats at the surface of the water. Their stems can reach 33 feet long. Their leaves are usually less than 2 inches long.

Ecology and Natural History: Eurasian water-milfoil is native to Europe, Asia, and Northern Africa. The species was most likely introduced intentionally for aquarium and nursery trades. Growth of horizontal roots can extend a colony, but stem fragments can create entire new colonies. Motorboat traffic creates fragments and distributes them within a lake or river. Transport on boating equipment introduces fragments to new waterbodies. Eurasian water-milfoil has been known to form hybrid plants with native Northern water-milfoil.

Impact of Introduction: Eurasian water-milfoil grows in dense colonies that compete and displace native plants. The colonies can form mats on the surface of the water that impede transportation and recreation. Millions of dollars have been spent nationwide on control efforts.

Oneida County Waterbodies with Eurasian Water-Milfoil: Bridge Lake, Clearwater Lake, Crescent Lake, Eagle River, Hancock Lake, Horsehead Lake, Kathan Lake, Kawaguesaga Lake, Lake Nokomis, Little Bearskin Lake, Lone Stone Lake, Long Lake, Manson Lake, Mid Lake, Minocqua Lake, Oneida Lake, Pelican Lake, Rainbow Flowage, Rice River Flowage, Squash Lake, Sugar Camp Creek, Tomahawk Lake, Tomahawk River, Townline Lake, Upper Kaubashine Lake, Virgin Lake, Willow Flowage, Willow Lake, and the Wisconsin River.