Willapa Bay is a bay located on the southwest Pacific coast of Washington state in the United States. The Long Beach Peninsula separates Willapa Bay from the greater expanse of the Pacific Ocean. With over 120 square miles (310 km2) of surface area Willapa Bay is the second-largest riverine estuary on the Pacific coast of the continental United States. Early settlers called the bay Shoalwater Bay and this name is found on old maps and charts of the region.