The Eurasion Water Milfoil

What it looks like:

Close view of one stem

Myriophyllum spicatum is an underwater plant with feather-like leaves. At each node along the stem, there are usually 4 stems coming out in different directions. Along each leaf, there are usually 12 or more leaflet pairs. The stems can grow up to 3 meters long. At first glance similar to "seaweed", it forms dense mats in the water either on the surface or a few feet under depending on how much it has grown and how deep the water is. In Lake Washington it is very easy to find and you can probably find it the next time you go to a dock or beach along the shore. Along the shore it can stretch for over a mile in some areas. (kingcounty.gov)

Water surface view

Where it's from:

Originating from Europe, Asia, and Africa it has invaded all over the world, being the most problematic in North America. The plant is able to spread so easily because it can stick to boats and trailers that travel from one lake to another. By using a reproduction process called "fragmentation", when the plant is broken into pieces each individual piece is able to sprout roots and become a whole new plant. This means that if only a piece of milfoil is on your boat when traveling to a new body of water, that one piece could potentially lead to millions of new milfoil in a previously vacant lake. (ecy.wa.gov)

(Original Figure: Timeline, Washington State Department of Ecology)

Eurasion Watermilfoil has spread to lakes spanning all of Washington State:

(Washington State Department of Ecology: Aquatic Plant Monitoring)

*Dark squares are where species was found