The 7,374 acres that comprise the George Washington Memorial Parkway provide habitat and protection for at least 55 species of plants and animals listed as rare, threatened or endangered in the States of Virginia or Maryland by their Natural Heritage Programs. These include 45 species of vascular plants and 10 animals (5 vertebrates and 5 invertebrates). Important habitat for these species can be found at Great Falls Park, Turkey Run Park, and Dyke Marsh in Virginia, at Glen Echo Park in Maryland, and on Theodore Roosevelt Island in the District of Columbia. Great Falls Park has the only know location in the State of Virginia for two of the rare plants found there and Turkey Run Park is the only known Virginia site for the Spectacled Nettle Moth (Abrostola urentis).

Many of these rare species are associated with rare plant communities of the Potomac River Gorge such as Bedrock Terrace Rim Xeric Forest and Bedrock Terrace Xeric Savanna. The natural areas within GWMP are so rich in biodiversity that they are not yet fully known. As recently as 1995 a species of Crustacean new to science, currently called Stygobromus sp. 15, was discovered at a freshwater seep within GWMP jurisdiction.