Sideling Hill Creek is home to a number of rare species and habitats, including the State and Federally Endangered plant, Harperella (Harperella nodosum). In Maryland, this delicate plant grows in streamside cobble and rock crevices here and on Fifteen Mile Creek.

Found at 13 sites scattered from Maryland to Georgia, Harperella is adapted to the annual rise and fall of river waters. Harperella seeds germinate, or broken pieces of the plant take root, during low summer flows. High winter and spring waters cover young plants, protecting them from cold and ice, and uprooting competitors.

The Nature Conservancy and Natural Heritage Program of Maryland and the Western Pennsylvania Conservancy have been working with private landowners to protect Harperella and other natural features of Sideling Hill Creek.