About the Puget Sound Institute

Introduction
Overview: Puget Sound as an estuary
Essay by: Christopher Dunagan
Today, we understand that estuaries—where freshwater and saltwater
merge—are among the most productive places for life to exist.
Sailing into Puget Sound in the spring of 1792, Capt. George Vancouver and his crew explored
the nooks and crannies of an uncharted inland sea, recording the location of quiet bays,
turbulent passages and all manner of rugged shoreline.
Two centuries later, cartographers still marvel at the precision of those first maps of Puget
Sound—one of the largest and most productive estuaries in the United States.
Archibald Menzies, assigned to study the plants and animals discovered on the voyage, classified
hundreds of “new” species, personally naming many of them. Menzies relished the variety of
plants he found, while the ship’s crew feasted on native oysters, crabs, salmon, trout and a new
species of flounder.
Long before Vancouver’s voyage, Native American culture embraced the bountiful flora and
fauna of the region. Local tribes knew where to hunt, fish and gather plants—and they had their
own names for places and things.
It would be nearly a century, however, before early ecologists began to understand that the
variety of living things described so carefully by Menzies was a direct consequence of the
physical associations among land, water and climate.
Today, we understand that estuaries—where freshwater and saltwater merge—are among the
most productive places for life to exist. Plant and animal communities thrive in these protected
areas of brackish water, where freshwater flowing from the land combines with seawater coming
from the ocean. In all, an estimated 2,800 streams— from large rivers to small creeks— flow into
Puget Sound.
Because salinity is a continuum from the freshwater rivers to the briny ocean, estuaries are not
defined by size. River deltas are considered estuaries, as are the larger bays, inlets and sloughs.
More broadly, Puget Sound is itself an estuary.
Complex food webs have evolved from the unique conditions found near the mouths of Puget
Sound’s rivers. Sediments dislodged from upstream areas and from shoreline bluffs provide the
substrate for plants, which flourish in the nutrients and sunlight of the shallow waters.
Geology, water depth, wave action, tides and river currents all influence the unique character of
an estuary, including whether the bottom is rocky, sandy or muddy. Conditions hostile to some
plants and animals are perfectly suited to others.
Young salmon migrating from rivers to the ocean linger in the estuaries, proceeding slowly as
their bodies adjust to the salty water that would kill many freshwater fish. On their return to the
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