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Learning to Be Vigilant

Updated: Feb 5, 2021

The following article was written by Larissa Cassano-Hamilton, Watershed Specialist with the Mercer County Conservation District and was originally included in the Summer/Fall 2020 edition of the "Tracking Invasive Species with Pennsylvania iMapInvasives" newsletter.

Eurasian water-milfoil. Credit: Alison Fox, University of Florida, (link)

In northwestern Pennsylvania, we are lucky to be surrounded by so much green (and blue) space - from farm fields, to game lands, to state parks with lakes and rivers. These great spots get more and more visitors that come and go throughout the season, especially now during the COVID-19 pandemic with outdoor recreation on the rise in the United States. However, sometimes visitors might accidentally take home more than just good memories and a nice-looking fish after visiting their local park or recreational area.

Aquatic invasive species (AIS) are plants and animals that can get stuck on gear and vessels and be easily introduced into other bodies of water via movement by humans or waterfowl. AIS can accidentally be transported on boats, pets, and recreational gear, and it's important for outdoor enthusiasts to be vigilant and check for aquatic hitchhikers whenever they are recreating on a waterbody. It's also recommended to take note of posted signs that display information about aquatic hitchhikers.

One species in particular, Eurasian water-milfoil (Myriophyllum spicatum), is an invasive aquatic plant that boaters and fishermen should be checking their gear for. Because it can spread via fragmentation, a single piece of this plant can begin a new population if transported to a new location.

Eurasian water-milfoil is a feathery, submerged aquatic plant that can quickly form mats in shallow areas of lakes and rivers in North America. These mats can then interfere with swimming and entangle propellers, which hinders boating, fishing, and waterfowl hunting. Heavy infestations may even reduce property values. Dense milfoil infestations can displace native aquatic plants, which negatively impacts fish and wildlife.

Eurasian water-milfoil line drawing. Credit: Minnesota Sea Grant

Eurasian water-milfoil was first introduced to North America through the aquarium trade in the 1940s from a European/Asian origin. It has since spread to nearly every U.S. state and several parts of Canada.

If a small piece of this plant remains on your gear, it could spread and establish in a new ecosystem if you frequent various waterbodies. Also, fragments of Eurasian water-milfoil that remain moist can be viable for weeks. The Pennsylvania Fish and Boat Commission and other agencies advocate "Check, Clean, Drain, Dry" when it comes to preventing the spread of AIS on recreational gear.

Note: If you see a large, dense mat of a single aquatic plant in a water body, it might be a good indication to do some research and reach out to an agency for more information. It might just be an aquatic invasive species.

Eurasian water-milfoil has already been found in several bodies of water across Pennsylvania. According to data in iMapInvasives, almost two thirds of all Pennsylvania counties have documented occurrences of Eurasian water-milfoil.

Additional Resources

  • Pennsylvania Sea Grant: Eurasian water-milfoil informational fact sheet

  • Pennsylvania Fish and Boat Commission: Clean your gear and prevent the spread of aquatic invasive species

  • Pennsylvania Department of Conservation and Natural Resources: Eurasian water-milfoil fact sheet (includes native look-alikes)

  • iMapInvasives: A free-to-use online clearinghouse that allows anyone with a registered user account to log findings of Eurasian water-milfoil and other invasive species


About the Author

Larissa Cassano-Hamilton is the Watershed Specialist with the Mercer County Conservation District (MCCD). In her free time, she enjoys creating recipes in the kitchen and spending time with her family. On weekends, she loves to explore the trails of Pennsylvania and beyond, together with her husband, and their pup, Duke. Larissa can be reached at


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