Once the Columbia River has dumped tons of sediment at its mouth, ocean currents carry it along 100 miles of coastline. Sand from the Cascades and beyond form beaches and dunes. Winds off the ocean shape sand into dunes, sometimes in the form of waves. Parts of the coastline are suffering erosion as a result of development during the past century.

Waikiki Beach is a flat sandy beach along the ocean side of Cape Disappointment, one of the warmest coastal beaches in the state, and the only beach considered safe for swimming on the Washington coast. Waikiki is named for Hawaiian sailors who drowned there a century ago, a few of the many victims of the rough “graveyard of the Pacific.” Its waves are less threatening now, as the large jetty at the river mouth partially protects the beach.