[2][3] It also protects sites dating as far back as the 17th century related to African-American history, as well as an ecologically and biologically important area of the Potomac River and its Maryland shoreline that supports many species of plants and animals.

The sanctuary's northern boundary then runs east across the Potomac River in a straight line until it intersects with the Maryland shoreline just north of Sandy Point.

[2][11] On occasion the ships anchored near Mallows Bay while awaiting scrapping burned, broke loose, or otherwise became hazards to navigation, so authorities ordered the company to secure them.

[11] After the United States entered World War II in December 1941, Bethlehem Steel began a third and final round of salvage that lasted for two years.

[2] Notable shipwrecks include Accomac (38°28′07.58″N 077°16′11.29″W / 38.4687722°N 77.2698028°W / 38.4687722; -77.2698028 (Accomac)), a former ferry abandoned at Mallows Bay in 1973 and the sanctuary's only steel-hulled wreck,[11][12] and Afrania (38°28′23.34″N 077°15′57.378″W / 38.4731500°N 77.26593833°W / 38.4731500; -77.26593833 (Afrania)),[11][13] Aowa (38°28′15.44″N 077°16′11.85″W / 38.4709556°N 77.2699583°W / 38.4709556; -77.2699583 (Aowa)),[11][14] Bayou Teche (38°28′28.16″N 077°16′08.16″W / 38.4744889°N 77.2689333°W / 38.4744889; -77.2689333 (Bayou Teche)),[11][15] Benzonia (38°28′13.94″N 077°16′11.06″W / 38.4705389°N 77.2697389°W / 38.4705389; -77.2697389 (Benzonia)),[11][16] Boone (38°28′20.28″N 077°15′59.07″W / 38.4723000°N 77.2664083°W / 38.4723000; -77.2664083 (Boone)),[11][17] Dertona (38°28′27.84″N 077°16′00.37″W / 38.4744000°N 77.2667694°W / 38.4744000; -77.2667694 (Dertona)),[11][18] Mono (38°28′23.95″N 077°16′13.94″W / 38.4733194°N 77.2705389°W / 38.4733194; -77.2705389 (Mono)),[11][19] Moosabee (38°28′28.16″N 077°16′02.89″W / 38.4744889°N 77.2674694°W / 38.4744889; -77.2674694 (Moosabee)),[11][20] Namecki (38°28′21.14″N 077°16′12.14″W / 38.4725389°N 77.2700389°W / 38.4725389; -77.2700389 (Namecki)),[11][21] and Yawah (38°28′28.63″N 077°16′15.06″W / 38.4746194°N 77.2708500°W / 38.4746194; -77.2708500 (Yawah)),[11][22] all of which were Emergency Fleet Corporation ships, and most or all of which have been in Mallows Bay since at least 1929.

[16] The stretch of the Potomac River in the Mallows Bay–Potomac River National Marine Sanctuary is part of the traditional homelands of the Native American Piscataway people of the Piscataway Conoy Tribe in Maryland and the Patawomeck people of the Patawomeck Indian Tribe of Virginia, to both of whom the area is of important cultural, historical, and spiritual significance.

[25] Shallow waters near the sanctuary's shoreline contain large beds of submerged aquatic plants which grow each year from late spring through early fall.

[25] Eastern redcedar (Juniperus virginiana), paw paws of the genus Asimina, persimmon trees, marsh tickseed (Bidens trichosperma), and pickerel weed of the genus Pontederia grow on the wrecks, providing a home for various animal species including ospreys, who visit the sanctuary each spring and summer and build their nests on the wrecks.

[13] A great variety of freshwater aquatic plants grows in the tidal marshes at the mouths of streams that flow into the Potomac River along the sanctuary's Maryland shoreline, where they absorb nutrients from runoff water, provide feeding grounds for many animal species, and prevent erosion of the shore.

[25] Broad-leaved emergent plants dominate these habitats, including green arrow arum (Peltandra virginica), pickerel weed, and spatterdock (Nuphar advena) at lower elevations and jewelweed of the genus Impatiens and wild rice at higher ones.

[25][26] Among other animal species commonly found in and near the sanctuary are double-crested cormorants, white-tailed deer, raccoons, northern watersnakes, northern red-bellied cooters, eastern box turtles, green frogs (Lithobates clamitans), spring peepers, American toads, spotted salamanders, zebra swallowtail butterflies, eastern pondhawks (Erythemis simplicicollis), and bumble bees.

[25] However, it is dominant in the Mallows Bay–Potomac River National Marine Sanctuary's waters, where it can grow very thickly, block sunlight, and crowd out native plants,[25] as well as obscure submerged historical resources.

[26] Drooping star of Bethlehem (Ornithogalum nutans), found on the wreck of SS Afrania, is reported as invasive in the Mid-Atlantic region of the United States, where it crowds out native plants on the floors of forests.

The buoy's data is of use to scientists and resource managers assessing environmental changes, which aids them in decision-making and other ecological restoration and historical preservation efforts.

[36] In the summer of 2020, the National Marine Sanctuary Foundation and the Potomac Riverkeeper Network established a partnership to create a citizen science monitoring program at Mallows Bay.

[38][39] The designation process for the Mallows Bay–Potomac River National Marine Sanctuary began on September 16, 2014, when Governor of Maryland Martin O'Malley submitted to the National Oceanic and Atmospheric Administration (NOAA) a nomination of the area for sanctuary status on behalf of the State of Maryland, Charles County, and a wide variety of community groups.

[2][7] The nomination advocated the sanctuary's creation to protect the historic shipwrecks and cultural heritage resources in the area, foster partnerships with educational and research groups and institutions, and improve public access, tourism, and economic development.

A three-month public comment period followed, during which NOAA solicited additional input on the scale and scope of the proposed sanctuary, including ideas presented in the community nomination.

NOAA used the public scoping comments in preparing regulations for the proposed sanctuary, the draft environmental impact statement, and other documents, all in close consultation with the State of Maryland.

Based on comments during this period, as well as internal NOAA deliberations, discussions with state-recognized Native American tribes, consultation with the United States Department of the Navy (which cooperated in the preparation of the environmental impact statement on behalf of four military facilities in the area), meetings with constituent groups, and an evaluation of these inputs with the State of Maryland and Charles County, NOAA chose the 18-square-mile (47 km2) alternative for the proposed sanctuary.

It is composed of 15 members and 15 alternates who represent various stakeholders in the sanctuary's affairs, including education, marine archaeology, maritime history, research, fishing, recreational, tourism, cultural resource, and economic development interests as well as the community at large.