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The Watershed

The Geography

The Cedar River/Lake Washington Watershed is, physically, the land area in which rainwater drains to Lake Washington and out through the Hiram Chittenden Locks in Ballard. The Cedar River/Lake Washington watershed includes the Cedar River and its tributaries, May Creek, Coal Creek, Mercer Island, Mercer Slough, Kelsey Creek, Fairweather Creek, Yarrow Creek, Juanita Creek, Forbes Creek, Lyon Creek, McAleer Creek, Thornton Creek, Ravenna Creek and of course, Lake Washington. The Cedar River/Lake Washington watershed is home to more than 83 species of fish and wildlife, including 14 species of concern, such as sockeye salmon, and the endangered Chinook salmon.  The watershed is considered to be some of the best remaining salmon habitat in King County.  


Wria 8 Map



The Cedar River itself is about 45 miles (72 km) long, originating in the Cascade Range near Abiel Peak, flowing generally west and northwest, emptying into the southern end of Lake Washington. The Cedar River flows through the Ship Canal, finally draining into Puget Sound through the Hiram Chittenden Locks. The upper Cedar River flows through a region of deep and porous glacial till. A large amount of water seeps into the ground, forming an aquifer. Most of this underground water eventually returns to the surface as springs, flowing mainly into the Cedar River as well as the Snoqualmie River and Rattlesnake Lake.

 The lower Cedar River basin is home to over 60,000 people, and includes the communities of Maple Valley, Ravensdale, and Renton. It is prone to flooding during large rain events. Look up Cedar River flooding information, including real time gauge data, and flood stage info, and learn what it means for the residents along the Cedar River.


Invasive Plant Species

There are currently several plant species that are considered highly invasive along the banks of the Cedar River.  Of particular concern are four species of knotweed, originally planted as an ornamental by local gardeners in the 1800's. It is now spreading aggressively throughout Puget Sound river systems. Through systematic treatment and community cooperation this plant can be controlled. For more information on our efforts to work with local land owners to control invasive species and restore native species along the Cedar River, please see our Stewardship in Action Program.


Watershed Image


The People

The watershed is home to 22% of the population in the state of Washington and includes the 98118 zip code, the most diverse zip code in the country, according to 2010 census data.  Over 94 different languages are spoken within the boundaries of the Cedar River/Lake Washington watershed.

There are over 30 cities in the watershed, including Bellevue, Brier, Edmonds, Kenmore, Lake Forest Park, Seattle, Renton, North Bend, Maple Valley, Mercer Island, Newcastle, Redmond, Sammamish, Shoreline, and Woodinville.  From a watershed perspective, each of these cities is connected to the health of one another and the greater whole. If you live in the Cedar River/Lake Washington Watershed, almost all of what you pour down the drain or into the ground eventually makes its way to the river, ultimately ending up in Lake Washington, each of these bodies of water make their way to Puget Sound.  The correlation between the people, the river, the lake, the sound, and the land is a close one.  The watershed is where we live and work each day.  It is where we raise our children, and the decisions we make today will be the legacy of the next generations.  Our guiding question is: How can we live sustainably in this place?  


The Municipal Watershed and our Drinking Water

 The upper watershed is a protected area known as the Cedar River Municipal Watershed. About 90,000 acres, or 143 square miles, is owned by the City of Seattle and managed as an ecological preserve to provide drinking water for about one million King County residents. The municipal watershed is one of only six protected watersheds in the country, and is the only municipal watershed owned by the people it serves.

It takes over 100 million gallons of water per day to fulfill the water needs of the communities that drink the waters of the Cedar. The forest acts as a kind of natural water filtration system. As a result, the Cedar River is one of the few rivers in the United States used for drinking water without requiring specially fabricated filtration. Chester Morse Lake is the main storage reservoir of the Cedar River Watershed system. Pipelines route water to the Seattle area from Landsburg Dam at the western edge of the protected watershed. Public access is restricted and the area is being managed to promote old-growth forest conditions in order to protect water quality. Costing rate-payers less than on- half of one cent per day, users of Cedar River water have access to some of the cleanest, least expensive, and best-protected water in the world.


Creation of a Unique System

Before 1912, the Cedar River did not empty into Lake Washington as it does today, but rather into the Black River. The Black River drained the southern end of Lake Washington, flowing south then west to join the Green River. The Black-Green confluence created the Duwamish River, which emptied into Elliott Bay. In 1911 the Cedar was re-routed, essentially disconnecting the Black, into the south end of Lake Washington to provide enough volume to power the Hiram Chittenden Locks.  This diversion was completed in 1912. The Cedar River's water, via Lake Washington, still ultimately flowed into the Black River, Duwamish River, and into Elliott Bay. 

In 1916 the Lake Washington Ship Canal's Montlake Cut was finished, connecting Lake Washington and Lake Union. The water level of Lake Washington dropped 8.8 feet to the level of Lake Union. As a result the outlet of Lake Washington became the Ship Canal instead of the Black River. The Black River dried up and no longer exists. Today the Cedar River's water enters Lake Washington and then passes through the Ship Canal and the Hiram Chittenden Locks to Puget Sound, rather than into Elliott Bay via the Duwamish River. 

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