Invasion of the European Water Chestnut!


By Gwen Supplee

I’d like to tell you about alien invaders…no, not Martians from outer space, but plants from the other side of our own planet.  In this case, it’s not an unidentified flying object we’re worried about, but an invasive floating plant.

The European water chestnut (Trapa natans) is an invasive, partially submerged aquatic plant that was introduced to the U.S. in the 1920s from Eastern Europe. It has spread through watersheds within the Chesapeake Bay watershed such as the Potomac River, Sassafras and Bird rivers of Maryland, and the lower Susquehanna River in Pennsylvania.  Recently, it has begun to impact smaller, local watersheds closer to EPA’s Philadelphia regional office where I work, such as the Perkiomen Creek Watershed in Montgomery County, Pennsylvania.

Why should you care – aren’t water chestnuts those yummy things that you can find in Chinese food? Not these water chestnuts! The European water chestnut consists of multiple rosettes, with long cord-like stems that can be as long as 16 feet, forming dense floating mats and making the waters  a pain for boating and fishing. As if impeding your recreation out on the open water wasn’t enough, the seedpods typically have four barbed spines that are sharp enough to penetrate shoes as you scamper in the shallow waters of impacted areas. Ouch!

waterchestnut2As far as the native ecosystem is concerned, the floating foliage severely limits the passage of light into the water, reduces oxygen levels in the water, and reduces growth of native aquatic species, all of which are needed to maintain a well-functioning aquatic ecosystem. And these water chestnuts are definitely not good to put in your salad or stir fry.

How prolific is this invasive plant? Each plant produces up to 20 seedpods per rosette and each seedpod can live for up to 12 years. In one year, one plant can produce 300 new plants! European water chestnuts prefer slow-moving and nutrient-rich waters, like man-made or natural ponds, and shallow creeks. The water chestnut begins to flower in late July.  The nuts ripen one month later and seed production continues into the fall.

What can you do to help stop the spread of these invaders? If there is European water chestnut (or other invasive aquatic plants) where you recreate:

Remove the aquatic plant from all parts of your boat, trailer, fishing gear and accessory equipment. Dispose of the removed material in the garbage.

Drain all water from your boat including your bilges, live wells, buckets and other water containers before leaving the water access area.

Wash your boat and gear thoroughly with regular tap water when you get home. Flush water through any part of the boat that contained water from the waterway including motor’s cooling system, live well and any other area that holds water. Dry equipment and boats in a sunny location before using them in a new body of water.

Volunteer with your local watershed organization if there is European water chestnut where you live.

waterchestnut3I recently had the pleasure of joining the Perkiomen Watershed Conservancy in Schwenksville, Pennsylvania, which is organizing hand-pulling parties all summer long, in order to remove the plant before it begins to flower and go to seed. Not sure whether you have a watershed organization where you live?

You can surf your watershed to find out. The best way to keep invasive plants out of our waters is to be informed about what species are a threat in our region and in the rest of the country.  Do you know of invasive plants in the waters where you live and recreate?