Estuaries, places where salt and freshwater mix, are some of the most biologically productive ecosystems on the planet. These tidally driven areas of transition between land and sea are home to a tremendous variety of plants and animals, are rich in nutrients and provide the basis for the food chain. The whole of Grays Harbor is an estuary.

Open water provides an area with abundant food resources for western grebes, double-crested cormorants, common loons and Caspian terns. Black brant feed on the eel grass beds and ducks feed at the waterline. Harbor seals hunt for fall Chinook and chum salmon.
 

Salt tolerant plants such as tufted hairgrass, Lyngby's sedge, Baltic rush and pickleweed surround the mudflat and provide cover and a resting place for birds during high tide. Saltmarsh plants also contribute small plant particles that fish and invertebrates consume. Plants also provide habitat for invertebrates and crustaceans. Ducks and geese nest and feed among grasses and sedges on the saltmarsh. Red-tailed hawks, merlin, peregrine falcons and northern harriers hunt prey over saltmarshes.
 

Twice a day, as the tide recedes, vast expanses of mud are exposed. Although it may not look like it, mudflats are a banquet table for birds. Within a square meter of mud, there may be up to 50,000 individual invertebrates! More than 90 percent of these tiny animals occur within the top five centimeters of mud. This abundant food resource enables shorebirds to gain up to 30 percent of their body weight in fat prior to resuming their travels. The tide refreshes mudflats with nutrients.