There's more to milfoil – Native aquatic plants support a healthy ecosystem

When Wesley Glisson started at Ecology’s Environmental Assessment Program as an aquatic plant specialist a few years ago, he found a folder of historical educational outreach materials left at his new desk. There was a landscaping tips booklet for people living near lakes, a coloring page about wetlands, and an eye-catching bright yellow bumper sticker.

Tucked away among the folders, the bumper sticker has a red STOP sign,

followed by green text saying, “…spreading milfoil around!” It has a line drawing of a sprig of Myriophyllum spicatum — an invasive watermilfoil. The plant has feathery leaves along a wavy main stem.

The sticker was a relic from a mid-90’s campaign to slow invasive Eurasian watermilfoil from further spreading from lake to lake on boat motors, trailers, and fishing gear. You might still see it on the bumper of an older car or boat trailer.

Impacts of an introduction

Eurasian watermilfoil photo by J. Parsons

Eurasian watermilfoil was brought to the U.S. as an ornamental plant decades ago. The state first became aware of it as an invasive plant in the 1970s.

Eurasian watermilfoil often grows to the surface where it spreads out, resulting in a tangle of spaghetti-noodle-like stems. This nuisance growth reduces the ability to enjoy the water for swimming, fishing, and boating. Declines in the recreational value of a lake from Eurasian watermilfoil invasion has even led to decreased property values for lakefront King County homes, according to a 2014 study. 

Eurasian watermilfoil has also been linked to reductions in beneficial native aquatic plants and fish species.

Since its discovery, Eurasian watermilfoil has spread to dozens of lakes throughout Washington, and we are still finding it in new lakes today. For this reason, it is important to clean, drain, and dry boats and equipment used in the water before heading to a new lake or river.

Mixed milfoil messages

As Ecology’s Aquatic Plant Specialist, Wes Glisson is often called on to assist with aquatic plant identification and control. While he appreciates the bumper sticker’s clear “stop milfoil” message, he worries that some nuance may have been lost.

“I think that this sticker may have helped to give native milfoils a bad rap,” Wes said. Growing just under the surface of many Washington lakes, six native milfoils also grace our waters.

Wes noted, “Our native watermilfoils are an important part of our freshwater ecosystems. They provide shade and fish cover and their leaves provide habitat for aquatic invertebrates.”

Part of a complete habitat

Calls about milfoil are common. “It’s impressive how many people I’ve met working in the field who know the name ‘milfoil,’” Wes said. Many common aquatic plant species such as water naiads, waterweeds, and pondweeds have been mistakenly reported to Wes as invasive milfoil.

“Sometimes I do find milfoil, and sometimes it is Eurasian watermilfoil,” he said, “but not always.”

Rake with native pondweed

“It often surprises people when I tell them they have one of our native watermilfoil species in their lake,” Wes noted, adding, “These often-overlooked aquatic plants are diverse, beautiful, and ecologically important to lake habitats in Washington.”

Conservation of our native watermilfoil species is challenging. It is hard to see beneath the water and difficult to tell the types of milfoil apart. Further, native species can hybridize with their invasive cousins, which can lead to loss of the native species.

Look beneath

Wes encourages people to look under the surface of their local lakes to explore the variety of plants there, though he knows it may be difficult.

View through a bathyscope

“Even for those interested in enjoying the aquatic plant community, the ripples from a light wind or the glare from the sun on a calm day preclude observation of the underwater flora,” he said, noting that wearing polarized sunglasses can really help reach what Wes calls, “maximum aquatic plant enjoyment.”

One of the best ways to view aquatic plants is by donning a mask and snorkel while swimming, but if you want to stay dry, you can peer into the water with a bathyscope, an underwater viewing tube. You can build a simple bathyscope using items you might find around the house.

Another everyday item — a standard garden rake — works exceptionally well to pull up a sample of plants. Make sure to give the rake a spin as you pull the plants up through the water so that none fall off.

Once you spot a plant, there are number of resources to help identify it. For quick photo-based identification, download an app like Seek by iNaturalist to help. You might also try the Burke Herbarium’s plant identification tool. This online tool lets you select certain plant characteristics and choose from a narrowed selection of photos.

Start seeing milfoils around

Milfoils have a column-like shape and feathery leaves. One quick way to tell Eurasian watermilfoil apart from other watermilfoils in Washington is to count the leaflets, the individual segments that give the leaves their feathery appearance. If you count 24 or more, chances are you have Eurasian watermilfoil.

Eurasian milfoil has more than 24 leaflets

Our most common native watermilfoil, northern watermilfoil, has fewer than 24 leaf segments, and the leaves are generally wider than those of Eurasian watermilfoil. Northern watermilfoil leaves splay outward from the stem when removed from water. Eurasian watermilfoil leaves are limp and collapse against the stem when out of water.

If you are still stumped and/or think you may have Eurasian watermilfoil on your hands, contact Wes Glisson through our Aquatic invasive plants technical assistance webpage, or reach out to your county noxious weed program for assistance.