The marine nearshore and intertidal environments can be particularly susceptible
to pollution, given their proximity to both point and non-point sources, such as
stormwater pipes, wastewater treatment plants, and freshwater creeks and streams.
Many of King County’s marine beaches are within parks and provide a source of
primary-contact recreation through wading, swimming, kayaking, fishing, and SCUBA
diving. Nearshore and intertidal areas are also important marine ecosystem
components, providing spawning areas for several species of forage fish and
important habitat for juvenile salmonids. Water-borne pathogens can potentially
cause disease in humans resulting from direct contact with the water during
recreational activities. Excess nutrients can potentially cause eutrophication
in nearshore areas or cause preferential growth of unwanted marine flora such
as sea lettuce (Ulva spp.), which can significantly
alter the habitat required by some forage fish and their predators.
King County monitors water quality monthly at
20 beach/nearshore stations
and one associated stream station, located in Puget Sound, Elliott Bay, and
Quartermaster Harbor. Seventeen of the beach/nearshore monitoring stations are
located along the western shoreline of King County, and three are located
on Vashon and Maury Islands. Ten beach stations are located onshore or in the
vicinity of King County wastewater treatment or conveyance facility outfalls.
These include the West Point wastewater treatment plant (2 stations),
the Brightwater treatment system, the Vashon wastewater treatment plant, the
Alki and Carkeek CSO treatment plants, and the South Magnolia, Denny Way, SW
63rd Street, and Barton Street CSOs. All 20 of the beach stations are monitored
nutrients, and salinity
. The one stream station located in Piper’s Creek is monitored for bacteria,
temperature, and nutrients. The Piper’s Creek stream monitoring station provides
background information for the beach station at Carkeek Park, which is located
at the mouth of the creek as it enters Puget Sound.
Beach water samples are collected at approximately knee depth by inverting sample
containers just above the water surface, then sinking the bottle down to
approximately 12-inches below the water surface. The bottles are not filled
completely in order to allow room for mixing.
Marine beach water quality, and other discrete water data, can be found here. Please contact
with any questions about the program.
Information for Marine Swimming Beaches