Friends of Dyke Marsh is a volunteer group dedicated to preserving, restoring and enhancing Dyke Marsh, a freshwater tidal marsh in Fairfax County on the Potomac River just south of Alexandria, Virginia. The Dyke Marsh Wildlife Preserve is administered by the National Park Service.

What Is Dyke Marsh?

The Dyke Marsh Wildlife Preserve is a freshwater, tidal marsh on the Virginia side of the Potomac River in Fairfax County. It is a unit of the George Washington Memorial Parkway, U.S. National Park Service. For more information, visit the NPS website at

Volunteers Identify Butterflies and Dragonflies

Eastern tiger swallowtail

In the spring, summer and fall of 2017, a team of volunteers conducted regular surveys of Lepidoptera (butterflies, moths and skippers) and Odonata (dragonflies and damselflies) in the Dyke Marsh Wildlife Preserve.  Here are a few examples of their sightings:  

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Good News on the Treated Pumpkin Ash Trees

ash inspection

Since 2015, working with the National Park Service, FODM has been trying to save some of the pumpkin ash trees (Fraxinus profunda) of the marsh that are being attacked by the invasive, lethal insect, the emerald ash borer (Agrilus planipennis) (See our longer article in “Marsh Life”). 

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New Plant Observed in Dyke Marsh

brown-eyed Susan

Several people observed brown-eyed Susans (Rudbeckia triloba) this summer, 2017, along the Haul Road.  It appears to be a new species of Rudbeckia for Dyke Marsh and this is the first photographic record of the species on George Washington Memorial Parkway (GWMP) properties.  The plant was last observed in GWMP in Great Falls Park in 1919.

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Monarchs Migrate through Dyke Marsh in the Fall


In the fall of 2017, the last generation of eastern monarch butterflies (Danaus plexippus) is migrating  southwest to the mountains of central Mexico.  Some of the butterflies are stopping to sip nectar from the masses of smooth beggartick blossoms blooming in Dyke Marsh.

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Ridding the “Beltway Wetlands” of Trash


On September 23, 2017, FODMers joined Northern Virginia Conservation Trust (NVCT) and Porto Vecchio volunteers on a kayak and canoe trash cleanup of NVCT’s newest property, a two-acre wetland at the confluence of Cameron Run and Hunting Creek on Alexandria’s southern border, just north of Dyke Marsh. The tidal wetlands, under the Beltway/I-95 ramps and elevated highways, are favorite sites for roosting gulls, migrating shorebirds and other birds, especially at low tide, an eBird “hotspot.”

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The Potomac River’s Submerged Aquatic Vegetation

Water stargrass

FODMers and friends learned about the importance, abundance and distribution of submerged aquatic vegetation (SAV) in the Potomac River on September 13, 2017, when Dr. Nancy Rybicki, U.S. Geological Survey aquatic plant biologist and hydrologist, spoke to 55 attendees.

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The FODM Fall Walk, Plants and More

Dr. Wells

On a walk that FODM announced as a “plant walk,” 25 Dyke Marsh enthusiasts enjoyed the flora, fauna and more on a balmy September 9, 2017, in Dyke Marsh.  Retired George Washington University botany professor Elizabeth Wells led the group along the Haul Road trail out to the boardwalk for almost three hours.   Ms. Wells depth of knowledge and the rich biodiversity of the marsh easily held everyone’s attention.

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Why That Bare Area? Tackling Invasive Plants

Bare area

Many visitors to Dyke Marsh who walk along the Haul Road trail have questions about the cleared area on the west side of the trail across from “Dead Beaver Beach.”The answer:  The National Park Service and FODM are creating a demonstration plat, clearing the area of a massive invasive plant infestation and eventually planting some native plants.

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Cardinal Flowers Brighten the Marsh

Cardinal flower

The bright, scarlet cardinal flowers (Lobelia cardinalis) blooming in Dyke Marsh in August and September 2017 are delighting many visitors, including migrating hummingbirds.  “The tube-shaped flowers have two lips, the upper having two lobes and the lower lip so fragile, many insects cannot land on the plant to reach the nectar,” according to the guidebook, Walking the Wetlands.

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The Two Clematis Plants of Dyke Marsh

Virgins Bower

A stand of native clematis, Clematis Virginiana, has been growing on a shrub along the “long bridge” (bridge 23) in Dyke Marsh on the Mount Vernon Trail.  This is not the same as the non-native clematis that FODM “weed whackers” try to control, a plant called sweet autumn clematis or Clematis Terniflora.  

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Cautious Hope for Marsh Wrens

Marsh wren

This year, 2017, there seem to be more marsh wrens (Cistothorus palustris) occupying the Dyke Marsh Wildlife Preserve than at any time since 2014 when FODMers last recorded this bird as a breeder.  Data from volunteers this year suggest there may be as many as five territorial males in the marsh.  This does not necessarily mean the population is recovering.  Avian males appear more willing to occupy degraded or marginal habitats than females and, sadly, we have had no reports of females alone or as part of a breeding pair in Dyke Marsh since 2014.   

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