An estuarine habitat occurs where salty water from the ocean mixes with freshwater from the land. The water is generally partially enclosed or cut off from the ocean, and may consist of channels, sloughs, and mud and sand flats. River mouths, lagoons, and bays often constitute estuarine habitat. Within any estuary, there is a salinity gradient that determines to a large extent what plants and animals are present. In Puget Sound, it is difficult to differentiate between marine habitat and estuarine habitat, since salinity fluctuates with the seasons and tides. The Department of Natural Resources established a geographical boundary in 1990, drawing a line from Green Point, on Fidalgo Island, to Lawrence Point, on Orcas, and calling all waters to the east estuarine habitat, and water to the west marine (with some exceptions: Dungeness Bay, Sequim Bay, and various coastal estuaries such as Grays Harbor and Willapa Bay).
Sources:
http://www.dnr.wa.gov/Publications/amp_nh_marine_class.pdf
http://www.ecy.wa.gov/programs/sea/shellfishcommittee/mtg_may08/Salmon_Recovery_Report.pdf
Overview
An estuary is a place where saltwater from the ocean mixes with freshwater from rivers and streams. Technically, this defines all of Puget Sound, but scientists have identified several types of "sub-estuaries" within the water body. These include pocket estuaries (or embayments), tidally-influenced rivers and wetlands and other areas near the shoreline connected with freshwater sources. This summary provides descriptions of these estuaries from the Washington State Department of Natural Resources, the Puget Sound Nearshore Partnership and others.
