Harbor Island is a small circular barrier island with very little maritime forest. The single family homes and condominiums are situated in the dune fields and thickets.

Because it is set back into St. Helena sound, the 3.0 km beach (includes .6 km new sandbar as of summer 2024) does not receive much wave energy. Despite this, a short portion of the central beach area is highly erosional with no dunes. One uninhabitable home is also located along this particular stretch of shoreline. However the beach is accreting on the northern and southern ends of the island and a large sandbar has formed on the southern end. This added approximately .6 km to patrol.

Harbor has had a project since 1993 and averaged 90 nests per season since 2019.