Puget Sound (/ˈpjuːdʒɪt/ PEW-jit; Lushootseed: x̌ʷəlč IPA: [ˈχʷəlt͡ʃ] WHULCH)[1][2] is a complex estuarine[5] system of interconnected marine waterways and basins located on the northwest coast of the U.S. state of Washington.

Puget Sound extends approximately 100 miles (160 km) from Deception Pass in the north to Olympia in the south.

[1][2] The USGS defines Puget Sound as all the waters south of three entrances from the Strait of Juan de Fuca.

[7] Kruckeberg's 1991 text, however, does not reflect the 2009 decision of the United States Board on Geographic Names to use the term Salish Sea to refer to the greater maritime environment.

During the third, or Vashon Glaciation, a lobe of the Cordilleran Ice Sheet, called the Puget Lobe, spread south about 15,000 years ago, covering the Puget Sound region with an ice sheet about 3,000 feet (910 m) thick near Seattle, and nearly 6,000 feet (1,800 m) at the present Canada-U.S. border.

At its maximum extent the Vashon ice sheet extended south of Olympia to near Tenino, and covered the lowlands between the Olympic and Cascade mountain ranges.

As the Vashon glacier receded a series of proglacial lakes formed, filling the main trough of Puget Sound and inundating the southern lowlands.

[13] As icebergs calved off the toe of the glacier, their embedded gravels and boulders were deposited in the chaotic mix of unsorted till geologists call glaciomarine drift.

Other sills that present less of a barrier include the ones at Blake Island, Agate Pass, Rich Passage, and Hammersley Inlet.

The Seattle Fault cuts across Puget Sound, crossing the southern tip of Bainbridge Island and under Elliott Bay.

[16] The United States Geological Survey (USGS) defines Puget Sound as a bay with numerous channels and branches; more specifically, it is a fjord system of flooded glacial valleys.

[3] Water flow through Deception Pass is approximately equal to 2% of the total tidal exchange between Puget Sound and the Strait of Juan de Fuca.

[23] and edible kelps like kombu (Saccharina latissima)[24] Among the marine mammals species found in Puget Sound are harbor seals (Phoca vitulina).

[34] Many bivalves occur in Puget Sound, such as Pacific oysters (Crassostrea gigas) and geoduck clams (Panopea generosa).

The Olympia oyster (Ostreola conchaphila), once common in Puget Sound, was depleted by human activities during the 20th century.

[35] In 1967, an initial scuba survey estimated that were "about 110 million pounds of geoducks" (pronounced "gooey ducks") situated in Puget Sound's sediments.

Among these are grebes such as the western grebe (Aechmophorus occidentalis); loons such as the common loon (Gavia immer); auks such as the pigeon guillemot (Cepphus columba), rhinoceros auklet (Cerorhinca monocerata), common murre (Uria aalge), and marbled murrelet (Brachyramphus marmoratus); the brant goose (Branta bernicla); seaducks such as the long-tailed duck (Clangula hyemalis), harlequin duck (Histrionicus histrionicus), and surf scoter (Melanitta perspicillata); and cormorants such as the double-crested cormorant (Phalacrocorax auritus).

Puget Sound is home to a non-migratory and marine-oriented subspecies of great blue herons (Ardea herodias fannini).

[37] Bald eagles (Haliaeetus leucocephalus) occur in relative high densities in the Puget Sound region.

[39] Dispatched in an attempt to locate the fabled Northwest Passage, British Royal Navy captain George Vancouver anchored on May 19, 1792, on the shores of Seattle, explored Puget Sound, and claimed it for Great Britain on June 4 the same year, naming it for one of his officers, Lieutenant Peter Puget.

[42] An Hudson's Bay Company expedition led by James McMillan in late 1824 was first non-Indigenous group to enter Puget Sound since George Vancouver in 1792.

[43] The first non-Indigenous settlement in the Puget Sound area was Fort Nisqually, a fur trade post of the Hudson's Bay Company (HBC) built in 1833.

[47][48] The first organized American expedition took place under the helm of Commander Charles Wilkes, whose exploring party sailed up Puget Sound in 1841.

[50] In 1888 the Northern Pacific railroad line reached Puget Sound, linking the region to eastern states.

[51] Washington State was admitted to the union in 1889 as part of the Enabling Act, and the regions borders have since remained unchanged.

[53] Over the past 30 years, as the region's human population has increased, there has been a correlating decrease in various plant and animal species which inhabit Puget Sound.

[56] The causes of these environmental issues are toxic contamination, eutrophication (low oxygen due to excess nutrients), and near shore habitat changes.

[56] On May 22, 1978, a valve was mistakenly opened aboard the submarine USS Puffer, releasing up to 500 US gallons (1,900 L; 420 imp gal) of radioactive water into Puget Sound, during an overhaul in drydock at Bremerton Naval Shipyard.