Stygobromus hayi is a rare species of crustacean known by the common name Hay's Spring amphipod. It is endemic to the District of Columbia in the United States, where it occurs only in Rock Creek, a tributary of the Potomac River. It is a federally listed endangered species, is listed as Endangered on the IUCN Red List, and as Critically Imperiled by NatureServe. This amphipod measures 10 millimeters (0.39 in) in length. Because it lives underground, it is white in color and eyeless.