What Is a Barrier Island?

Barrier islands form as ocean waves continuously build up sand and sediment along coasts. Changing weather, wind, and the shape of the land keep these islands in constant motion. They may shift, erode, grow larger, or even disappear completely over time.

These islands usually lie parallel to the mainland. Lagoons, bays, or tidal channels typically separate them from the coast. The ocean side has beaches and sand dunes, while the landward side often has marshes, tidal flats, and coastal forests. These environments provide important habitats for nesting sea turtles, shellfish, fish, and seabirds.

Geography plays a major role in where barrier islands form. They often appear along flat coasts with low tectonic activity and nearby river deltas. Chains of these islands line the U.S. East Coast, including North Carolina's Outer Banks, and the Gulf Coast. In contrast, the U.S. West Coast lacks these islands because of active tectonic plates, steep rocky cliffs, and different tidal patterns.

Barrier islands also protect mainland communities and ecosystems from severe storms. Dunes and coastal grasses absorb incoming wave energy. This reduces storm surges and decreases flooding along the shore. However, barrier islands are currently losing land at an alarming pace. Human activities, including vessel traffic, hard levees, dams, and dredging, restrict the flow of sand and sediment that the islands need. Rising sea levels and stronger weather caused by climate change also speed up coastal erosion. To fight these losses, the National Oceanic and Atmospheric Administration (NOAA) supports restoration that uses nature-based infrastructure. Projects linked to Deepwater Horizon oil spill recovery in the Gulf of Mexico have restored or improved thousands of acres of barrier islands and marshes. These projects repair damage to natural resources while also strengthening coastal defenses and protecting estuary ecosystems.

How do barrier islands help wildlife and people, and what is causing many of them to lose land?