The sanctuary extends from the mean high tide line in Maryland state waters across the Potomac River to the mean low tide in Virginia state waters. The tidal freshwater river that comprises the majority of the sanctuary supports species of ecological, economic, and cultural importance, while the shipwrecks of the Ghost Fleet serve as islands of life that provide structure and habitat. Adjacent to sanctuary waters, Maryland’s Mallows Bay Park hosts wetlands, meadows, and forests that have been identified as highly significant for biodiversity conservation, habitat connectivity, and rare species and wildlife habitat.

Ghost Fleet

Outline of shipwrecks along the Mallows Bay shoreline that are filled with vegetation.
These remnants of World War I shipwrecks are known as the Flower Pot Wrecks. Photo: Duke University Drone Survey/NOAA

Nature has transformed the shipwrecks of the Ghost Fleet into a series of distinctive islands, intertidal habitat, and underwater structure critical to fish, birds, and beavers. Over time, sediment and seeds gathered inside the hulls of several of the ships, turning them into human-made islands that are often referred to as “flowerpot” wrecks. Several of these wrecks serve as an extension of the land, stabilizing the shoreline and providing a place for lush plant life to grow. Terrestrial species like paw paw, red cedar, and persimmon trees can be seen on the wrecks, as well as marsh plants like marsh tickseed and pickerel weed. This habitat provides a home for several species, such as ospreys who build their nests on the wrecks, or beavers that have built a lodge in an unidentified vessel. Ultimately, these ships have turned into a vital part of the local ecology, allowing nature to thrive.

Tidal River

Blue sky with white scattered white clouds top a shoreline section of Mallows Bay with outlines of shipwrecks in the water.
Aerial view of the shoreline along Mallows Bay. Photo: Kevin Olson/NOAA

The sanctuary is located in a transition zone, where the freshwater of the Potomac River mixes with saltwater of the Chesapeake Bay through daily tides that fluctuate from 1–2 feet. The water is largely fresh, with a salinity that typically ranges from 0.1–0.5 parts per thousand. The sanctuary waters support a variety of fish populations, such as largemouth bass, blue and channel catfish, striped bass, shad, river herring, and sturgeon.

From the late spring to early fall, the shallow waters near the shoreline contain large beds of submerged aquatic vegetation (SAV), or underwater grasses. They form grassy meadows and weed beds that serve as important feeding grounds and spawning and nursery habitat for juvenile fish, crustaceans, mollusks, and other animals. There are approximately ten different species of SAV that can be found in the sanctuary, including wild celery, water stargrass, coontail, and several species of naiads. A non-native grass called hydrilla, which was introduced to the Potomac River in the 1970s and 80s, is also dominant. While hydrilla offers some benefits and is protected in the Chesapeake Bay, it can grow very thick and crowd out native grasses.

Tidal Marsh

Trees full green leaves on either side of a small creek with muddy water.
An overview of a creek running through Mallows Bay Park. Photo: Kevin Olson/NOAA

At the mouth of streams that flow into the sanctuary along the shoreline, diverse freshwater marsh plants grow. In the low marsh near the water, lower elevation zones are dominated by broadleaved emergent plants, such as a spatterdock, green arrow arum, and pickerelweed, while higher zones support wild rice and jewelweed. In the late summer, you may also see the pink or white blooms of the swamp rose mallow, a marsh plant that may have inspired the name of the sanctuary. These marsh plants offer habitat and food for many species, absorb nutrients from runoff water, and help prevent erosion along the shore. Throughout Charles County’s Mallows Bay Park, trail signs highlight the cultural significance of these plants.

Wetlands

Water with grass and plants surrounded by trees and a lush green field.
Wetland area in Mallows Bay Park. Photo: McIntosh/NOAA

Beaver activity in the sanctuary creates unique wetland habitat. In a cycle that lasts many years, they will move up and down the streams that flow into the sanctuary and create dams, flooding different areas and drying out others. The nontidal wetlands that form behind the dams support floating aquatic plants, including spatterdock, white water lily, duckweed, and pondweed. Pickerelweed, rice cutgrass, sedges, and cattails often border the areas of open water behind beaver dams. These wetlands provide habitat, regulate the flow of water, and help prevent flooding and erosion.

Meadow

green plants with white flowers growing abundantly in a meadow surrounded by trees
A meadow located in Mallows Bay Park. Photo: McIntosh/NOAA

Meadows throughout Mallows Bay Park, managed by Charles County, contain a variety of grasses and wildflowers, such as broomsedge, goldenrod, milkweed, asters, and fleabane. These plants provide cover, food, and nesting sites for songbirds, insects, and small mammals. Efforts to restore native plants in these meadows are underway, as they are critical to bees, butterflies, and other pollinators.

Temperate Forest

A dirt trail going through the center of the picture which is surrounded by trees and floor vegetation.
Hiking trail goes through the temperate forest in Mallows Bay Park. Photo: McIntosh/NOAA

The forest in Maryland’s Mallows Bay Park varies, from the floodplain forest bordering streams and ponds through the drier, upland forest at higher elevations. In the floodplains, red maples, sycamores, and other flood-tolerant trees grow. Smaller, broad-leaved paw paw trees are also common in the understory. A secondary succession forest has developed in the agricultural land that once belonged to Wilson Farm, dominated by young trees such as sweet gum. The mature upland forest contains oaks and pines, with shrubs such as mountain laurel and blueberries in the understory.