Sand Island is just that, a pile of sand. It was created and is maintained through the disposal of sand dredged to create a boat channel. The island has a maximum elevation of about ten feet. Repeated disposal and storms eliminate most vegetation. The little vegetation that is present is typical of coastal dunes.
Although artificially created, Sand Island functions as a barrier island. It is in the Gulf of Mexico, several miles from the mainland. It is part of the chain of barrier islands that includes Cat, Ship, Horn, and Petit Bois Islands, and is part of the Gulf Islands National Seashore.
Sand Island is the only place in Mississippi where Gull-billed Terns, Royal Terns, and Sandwich Terns nest. Unfortunately it is not used every year. These species commonly change nesting sites from year to year, and the factors causing them to abandon Sand Island in some years are unknown. When it is used, the nesting colonies can be large. 1,850 pairs of Sandwich Terns nested in a single colony on the island in 1998.
Sand/mud flats around the island are heavily used by feeding shorebirds and wading birds.
The National Park Service closes the island to public access during the nesting season to protect nesting terns and skimmers. However, the remote location makes enforcement difficult.
National Park Service monitors and manages the island.