Grays Harbor is an estuarine bay located 45 miles (72 km) north of the mouth of the Columbia River, on the southwest Pacific coast of Washington state. The bay is 17 miles (27 km) long and 12 miles (19 km) wide. It is a ria, which formed at the end of the last ice age, when sea levels flooded the Chehalis River.

Grays Harbor National Wildlife Refuge is located on 1,500 acres (6.1 km2) of intertidal mudflats, salt marsh, and uplands around Hoquiam. It is one of four major staging areas for migrating shorebirds in the Pacific Flyway. Up to one million shorebirds gather here in spring and fall. Grays Harbor is designated as a Western Hemisphere Shorebird Reserve Network Site, recognizing this internationally-significant shorebird habitat. As many as 24 species of shorebirds use Grays Harbor National Wildlife Refuge, with the most abundant species being western sandpiper and dunlin. Semipalmated plover, least sandpiper, red knot, and black-bellied ploverare also common during migration. The refuge is also used by peregrine falcon, bald eagle, northern harrier, Caspian tern, great blue heron, songbirds, and a variety of waterfowl.