The irregular bay side shoreline of these islands does not have longshore currents. Instead, the irregular shoreline is formed from sand piled up during storm wash-overs and sand blown landward by the wind. During fair weather conditions at Fenwick Island, especially in the summer, there is a slow persistent movement of sand to the north in response to prevailing waves from the southeast. The sand is carried along by the longshore current moving northward. On an annual basis, the balance between the northward drift and southward drift results in a net movement of approximately 150,000 cubic meters of sand to the south.
Jetties are rigid shore protection structures that extend from the beach into the surf zone.
They are built perpendicular to the beach to trap moving sand. These structures, which interrupt not only the flow of sand, but of the longshore current as well, commonly bring about consequences for the adjacent beaches. All flowing water, such as a longshore current, has a carrying capacity for sediment related to its velocity. If sediment is available, as it is along a beach, the current will carry its capacity amount. If sediment is not available, the current will pick up sand from the next available location, to once again fill its carrying capacity.