King County rivers and streams

The diversity of streams in the county is a reflection of the diversity of its geography. From the small rivulets that begin high in the Cascade Mountains, to the brooks that flow gently across the lowlands, to the five major rivers of the county, there are over 4,800 kilometers (3,000 miles) of perennial streamcourses in King County.

Despite the impressive total length, King County has no rivers that are longer than 150 kilometers (93 miles). For two of the rivers—the South Fork of the Skykomish and the White—only a portion of their length flows through King County. But geography has as much to say about river length as jurisdiction. The distance from the Cascade Crest to the shores of Puget Sound is short and the valleys that carry the major rivers are glacially carved, narrow, and relatively straight. From north to south, the major rivers of the county (total length of the river is in parentheses) are: The South Fork of the Skykomish (51 kilometers; 32 miles), the Snoqualmie (130 kilometers; 81 miles), the Cedar (90 kilometers; 56 miles), the Green-Duwamish (at 150 kilometers, 93 miles, the longest), and the White (122 kilometers; 76 miles). (See Landscape Diversity map for major rivers in King County.) Each of these has its headwaters in the Cascade Mountains, where they tumble down the steep terrain from snowfields and glaciers through narrow, steep-walled canyons into low elevation glacier-carved valleys, and finally flow alone or as tributary into larger rivers, then into Puget Sound. Along this path from mountains to Sound, each watercourse picks up numerous tributaries that drain the foothills and lowlands. A few small streams drain coastal lowland areas and empty directly into Puget Sound.

South Fork Skykomish River

The South Fork Skykomish River begins in the steep, heavily forested, deep-snow country of the Cascades near Thunder and Spark Plug Mountains in NE King County. The river flows generally west and northwest for about 32 miles (51 kilometers) to its confluence with the North Fork Skykomish River, in Snohomish County (the county directly north of King). The river is a part of the larger Snohomish River system that empties into Puget Sound at Everett, Washington.

All along its 32-mile (51-kilometer) course, the South Fork river picks up numerous moderate-sized tributaries, which are all important to the anadromous and resident salmon populations of this drainage. These include the Foss and Miller Rivers from the Alpine Lakes Wilderness from the south, the Beckler from the north, and Index and Money Creeks farther downstream. The South Fork and its major tributaries possess mountain-stream characteristics: moderately steep gradients, extensive rock and cascade channel forms, with deep pools and clear, cold waters. Where the gradients are not as steep, the mainstem South Fork and its tributaries are the major spawning and rearing areas for Chinook salmon in the greater Snohomish watershed and are home to bull trout and Dolly Varden, chars of the genus Salvelinus.

In its lower reaches, the South Fork flows through a deep, gravel-bedded valley typical of river valleys below the west slope of the Cascades. Here the river’s slope moderates and the stream takes on a more sinuous character. Gone are the bedrock cascades and chutes, and in their place are rapids and riffles of boulder and cobble. Steelhead and cutthroat trout make use of small pools of quiet water immediately downstream of these large blocks of stone. Occasional large jams of logs create low dams that slow the river’s flow and allow gravel to accumulate on the rough bed. These areas are the spawning sites for anadromous fishes. The jams also create most of the deep pool habitat found in the river by forcing the river to cut deeply into the bed and banks; these pools are refuge and rearing habitat for the offspring of the salmon.

The South Fork Skykomish River flows north and out of King County near the community of Baring at the foot of the Cascades. Here it joins the North Fork Skykomish to become the mainstem Skykomish River. From the forks, the Skykomish River flows another 48 kilometers (30 miles) to join the Snoqualmie River to become the Snohomish River near the town of Monroe in Snohomish County.

Snoqualmie River

A companion river to the Skykomish system, the Snoqualmie River has its headwaters in the high and snowy Cascades as well. The Snoqualmie has its headwaters near Le Bohn Gap below the glaciers of Mt. Hinman. From there the river flows approximately 81 miles (130 kilometers), first as the Middle Fork, then as the mainstem Snoqualmie. The mainstem Snoqualmie then meets the Skykomish River to form the Snohomish River. Along the upper part of its route, the river picks up tributaries—the Taylor and the Pratt and two other forks, the North Fork Snoqualmie and the South Fork Snoqualmie—before dropping 82 meters (268 feet) over Snoqualmie Falls to the valley below. These upper rivers are steep and swift, and car-size boulders and bedrock ledges are common. In the occasional broad parts of the narrow upper valley, the river braids and slows, gravel beds form and pools deepen; these stretches are home only to resident cutthroat and introduced rainbow and brook trout. Snoqualmie Falls is a complete barrier to anadromous salmon upstream migration. Regular suggestions are made to provide some sort of passage or transport for anadromous fish above the falls but no action has been taken. If this were to occur, the implications for native biodiversity in the upper watershed are likely to be significant.

Below the falls, the character of the river changes dramatically from mountainous to lowland, and the river meanders slowly northwest across a broad, flat valley floor another 58 kilometers (36 miles) to its confluence with the Skykomish River. Across the valley floor, the river has extensive gravel bars and glides but very few deep pools. Along its valley length lie farms and fields, and much of this portion of the river is revetted  (35 percent of the left bank and 30 percent of the right bank). Small amounts of large wood, so important to the formation of salmon habitat, can be found here, but not a single large jam occurs on the river. Like many other lowland rivers in King County, the jams were removed earlier in the century, sometimes for navigation, occasionally for firewood, most recently for flood control. Nevertheless, the mainstem is important habitat for populations of Chinook salmon, pink salmon, chum salmon, and steelhead. Along its lowland course, the river picks up several tributaries from the foothills along the river: Griffin Creek, the Tolt River, Harris Creek, and Cherry Creek from the north; the Raging River and Patterson Creek from the south. The major river tributaries tend to be relatively steep, but they still provide extensive habitat for Chinook, chum, and coho salmon. The lowland tributaries have lower gradients, and often their headwaters are in large beaver ponds and wetlands in the uplands. The combination of gentle gradient and ponds provides excellent conditions for coho salmon. In fact, these lowland tributaries of the Snoqualmie produce more coho salmon in a single year than any other comparable system in the state of Washington.

Cedar River

The shortest river wholly contained within the county is the Cedar River. The Cedar begins as the North Fork Cedar at Lost Lake on the slopes of Meadow Mountain in east-central King County and flows approximately 90 kilometers (56 miles) to Lake Washington in the lowlands. Along its route, it passes through the moderately steep mountain terrain of the upper Cedar River watershed for about 23 kilometers (14 miles) until it reaches Chester Morse Lake, the storage reservoir for the water supply for the City of Seattle. Above Chester Morse Lake, the river has three main tributaries: the Rex River and the North and South Forks of the Cedar. The 9.7 to 11.3 river kilometers (6 to 7 river miles) above the lake present excellent pool and riffle profiles as the slope of the channel moderates and the valley widens a bit. The streamside vegetation through this reach has improved greatly since the logging days of the early 20th Century. The City of Seattle is managing the watershed (and has been for the last 20+ years) for mature forest conditions and has developed a habitat conservation plan for the watershed that addresses terrestrial and aquatic ecosystems and their inhabitants.

From the dam at the outlet of the reservoir, the river travels through a canyon-like reach for two miles. The channel gradient is steep here, with numerous falls and cascades and a boulder-dominated stream bottom. The valley walls recline a bit for the next 10 kilometers (4 miles), but the valley remains narrow and steep-walled. The channel moderates and the streambed is rubble and large cobble with occasional rapids and deep pools. For the next 13 kilometers (8 miles)—until the Landsburg Diversion Dam—the valley alternately narrows and widens, the gradient moderates, and the streambed is mainly large gravels and rubble with many long, deep pools and broad gravel riffles. The streamside has reforested well from old timber operations, and the forest is mixed conifer and deciduous. At the Landsburg Dam, water is diverted into a pipeline for transport to Seattle, approximately 35 kilometers (22 miles) downstream.

From the diversion dam, the Cedar winds west and northwest through a shallow, narrow valley, through increasingly intense residential development, for about 19 kilometers (12 miles) until the valley widens dramatically. The gradient is moderate through most of this reach—except for the steeper upper 1.6 - 3.2 kilometers (1 - 2 miles)—and occasional steep gravel walls occur throughout. These walls, some 150 feet high, are the primary sources of the spawning gravels for this section of the river, and the most intense spawning activity of the river is observed through this long reach. Chinook, coho, and abundant sockeye salmon spawn in the mainstem throughout. Taylor Creek and Rock Creek are small but important spawning streams in this reach.

Below this section, the Cedar River winds westerly for 11 kilometers (7 miles) to its confluence with the southern end of Lake Washington. The valley is quite broad and flat, and intense residential development occupies the valley floor and the plateaus above the valley. Commercial uses cover the valley floor over the last mile or so to the lake. Much of the riverbank in the last 4 miles has revetments to prevent the river from meandering and threatening homes and businesses; the entire south bank is a railroad embankment. A recent landslide in the lower half of this reach has formed some of the best salmon habitat in the lower river, and fishery agencies and County biologists are working together to protect the slide in its present condition. The river receives heavy recreational use throughout this reach and the reach above, and the logs and debris naturally delivered into the river may present barriers and sometimes be hazardous to boaters. Where the river exits its valley, the Cedar is channelized for the last 3 kilometers (2 miles) or so to Lake Washington. This channel was constructed at the time the Cedar was diverted from its original confluence with the Green River; this diversion occurred in 1916  to supply water for lock operation in the Lake Washington Ship Canal (for more information, see below).

The Cedar River is home to several species of salmonids and, for its size, supports abundances that are among the greatest in the state. Sockeye salmon, once rare to potentially non-existent in the system, have reached upwards of 600,000 adults in recent strong years; coho salmon use almost all accessible tributaries in the Cedar, and Chinook salmon spawn beneath the gravel walls of the middle reaches (Chinook have not been as abundant in recent years, however, and many scientists are concerned for their survival). One species—the pygmy whitefish—is found in King County only in Chester Morse Lake and the Cedar River above the lake. An isolated population of bull trout also make use of the Cedar River and Rex River above Chester Morse Lake (see fish discussion in Section 1.3).

Lowland Streams of the Lake Washington Watershed

In addition to the Cedar River, which flows into the southern end of Lake Washington, the larger Lake Washington Watershed also contains a number of lowland streams that enter its northeastern tributary, the Sammamish River, and its companion lake, Lake Sammamish, which lies immediately over a ridge to the east of Lake Washington (see Landscape Diversity map). These streams include: Issaquah Creek, which drains the foothills of Tiger and Taylor Mountains and enters Lake Sammamish at its southern end; Big Bear Creek, which drains the flatlands to the north of Lake Sammamish and enters the Sammamish River just downstream of the lake; and Little Bear, North, and Swamp creeks, all lowland streams that enter the Sammamish River and typify the lowland streams of the county and, indeed, all of the Puget Lowland (see Riparian discussion in Section 1.3).

Issaquah Creek is somewhat of an exception to the lowland stream type in King County because its headwater tributaries, Holder Creek and Carey Creek, rise on the western and northern slopes of Tiger Mountain at about 460 meters (1,500 feet) elevation and flow swiftly down to the main valley floor. On the valley floor, Issaquah Creek possesses a shallow gradient and has the quintessential pool/riffle character of highly productive coho salmon streams. During the mid 20th Century, this valley was lined with small farms and fields. However, the decline of agriculture in this valley has allowed the regrowth of a dense riparian zone of alder and young conifer. The upslope streams, Fifteenmile and Holder creeks, are small and steep with occasional cascades and falls that limits the upward migration of anadromous salmon, but resident cutthroat trout are found above many of the barriers. Genetic analysis suggests that these populations may have been isolated from their lowland kin for 7,000 to 9,000 years, probably as a result of the decline of the glacial meltwater flow from alpine glaciers far to the east. Issaquah Creek’s lowland valley, which is very broad and flat for the size of the present stream, is a remnant of that glacial flow. The fishes found above the present-day falls may have found their way into these streams at that time. In addition to these native trout, Issaquah Creek has populations of Chinook, coho, steelhead, and sea-run trout in its mainstem, and sockeye salmon in its East Fork. The lowermost reach passes through the City of Issaquah, where a State of Washington salmon hatchery is located. During the upstream migration of salmon in the fall and winter, the hatchery uses a shallow weir to divert Chinook and coho salmon adults from the stream into holding ponds for use in an artificial propagation program. The adult salmon are sorted, eggs are taken from the females and milt taken from the males. Any salmon that are in excess of the number required to satisfy the production goal are then released into the creek above the weir. Sockeye salmon, a species that are not propagated in this hatchery, tend to migrate upriver about the same time as Chinook; these fish are passed through the weir without diversion.

Big Bear Creek is typical of the low-gradient, meandering character of King County’s lowland creeks. Like the others, Big Bear Creek rises from a small headwater lake and wetland that are set amid second- or third-growth forest in a watershed that is becoming increasingly urban. Big Bear Creek flows through many wetlands—old beaver ponds in its upper half—for about 19 kilometers (12 miles) to its confluence with the Sammamish River. Along its path, Big Bear Creek flows from headwater forests and wetlands, alongside a golf course, through an occasional subdivision, past old farms and horse pastures, and, finally, through urban development before it enters the Sammamish river. Despite the urbanization and other development, the creek retains considerable habitat for salmon: Chinook, sockeye, coho, and cutthroat trout are found throughout the stream, even into its uppermost reaches. Until recently, Big Bear Creek was the most productive stream for coho salmon in all of Puget Sound. Portions of the stream have some rather unusual inhabitants, including freshwater sponges and the largest populations of the western pearlshell mussel (Margaritifera falcata) remaining in King County.

Several streams occupy the lowlands to the west—Little Bear, Swamp, and North Creeks—and are quite similar in slope, morphology, and size to Big Bear, but their watersheds have experienced far more development than that of Big Bear. Nevertheless, coho salmon and cutthroat trout continue to find suitable habitats in these streams, and their presence is indicative of the resilience and tenacity of the family of salmonids.

Green-Duwamish River

The Green-Duwamish River originates in the high Cascades in the vicinity of Blowout Mountain and Snowshoe Butte, about 48 kilometers (30 miles) northeast of Mt. Rainier. From its headwaters, it flows approximately 150 kilometers (93 miles) to Puget Sound; it is the longest river in King County. For its uppermost 40 kilometers (25 miles), the river flows through narrow steep-walled valleys and heavily forested terrain of the upper Green River watershed. The stream flow over waterfalls and steep cascades for its first 16 kilometers (10 miles) until it meets Sunday Creek, the main tributary in this landscape. From here for the next 24 kilometers (15 miles), the valley widens and flattens, and dense stands of bottomland conifers and deciduous trees line the river. The valley walls are still steep and densely forested; the area is used primarily as a watershed for the City of Tacoma’s water supply. Some clearcuts are evident on the valley slopes, but that activity has slowed in the last decade.

Flowing through this rugged landscape, the Green River receives several tributaries: Friday Creek, Sawmill Creek, Champion Creek, Smay Creek, and Charlie Creek.

At about river kilometer 109 (river mile 68), 40 kilometers (25 miles) from the headwaters, the river enters Howard Hanson Reservoir, a flood control reservoir created by the US Army Corps of Engineers’ Howard A. Hanson Dam in Eagle Gorge at river kilometer 103.8 (river mile 64.5). The North Fork of the Green River is the major tributary to the reservoir. Three miles below the storage dam, the City of Tacoma maintains a water supply diversion structure (Tacoma Headworks). This facility represents the present upper limit of access for anadromous fish in the Green River.

Below Howard A. Hanson Dam and the Tacoma Headworks, the river enters the Green River Gorge, a steep-walled, forested canyon known for its whitewater. The river is moderately steep throughout the gorge, with plunges and drops among boulders and rock shelves. Much of the land in this area is owned by Washington State Parks, and King County has property holdings in the gorge as well. After 26 kilometers (16 miles), the Green River emerges into the broad river valley of the lowlands. From here the river meanders over a broad valley floor through an agricultural area with a few stands of deciduous and conifer trees lining the banks. Major lowland tributaries enter the Green River in this reach: Newaukum Creek, Crisp Creek, Burns Creek, and Soos Creek. Portions of the river are revetted here, but the County owns considerable land  where the river is free to meander naturally across the valley floor: Metzler and O’Grady Parks contain some of the finest river habitat features remaining in the Green River watershed.

Downstream at about river kilometer 42 (river mile 26), the Green River enters the lowland urban area of King County. From here to the river’s mouth in Elliott Bay, the river has been extensively channelized and diked. In its lower 16 kilometers (10 miles), the Green River is called the Duwamish River and is surrounded by the industrial heart of King County. In this area, the river once received three major tributaries: the White River, the Cedar River, and the Black River. Each of these tributaries has been rechanneled out of the Green River system, and these diversions have reduced the normal river flow by a third. First, the White River was channeled out of the Green in 1915, after a large flood in 1906 deposited a log jam that forced the White south into the Stuck River, a tributary to the Puyallup River. After long and arduous negotiations, its flow was transferred permanently into the Stuck River and the Puyallup River to the south. The Cedar River was diverted out of the Green-Duwamish River and into Lake Washington in 1916 to provide water to operate locks on the newly constructed Lake Washington Ship Canal. The opening of this same canal lowered Lake Washington by 2.4 meters (8 feet) and dried up the Black River, which was once the lake’s outlet to the Green-Duwamish River.

No other river in King County has undergone the level of transformation that has characterized the Green River, and despite all these changes, salmon continue to return to spawn every year. After the closing of Howard A. Hanson Dam in 1963, salmon could no longer migrate into the upper watershed through Eagle Gorge. This area was once the major spawning ground for steelhead, and possibly for a spring run of Chinook salmon (there is some disagreement among experts on this question). At the present time, migrating salmon are stopped at the Tacoma Headworks. Juvenile Chinook from a hatchery program are trucked above the dam, however, to make use of the rearing capacity of the upper watershed (and this program explains the distribution of Chinook on the Rare, Threatened, and Endangered Species map). In a few years, as part of an enhanced water storage project undertaken by the Corps of Engineers and the City of Tacoma, a fish lift will be installed to pass adult salmon above the dam. In the meantime, Chinook continue to use the river below the dam for spawning and rearing, especially the reach below the Green River Gorge downstream to the urban area. Chum salmon use this reach as well but mainly occupy the side channels of the middle Green. In recent odd-numbered years, a large population of pink salmon has established itself in the Green River to the surprise of many fishery biologists. This population was expected to reach nearly one million in early 2007.

The lowland tributaries of the Green River tend to be very low-gradient systems that flow along the valley floor (Burns and Crisp creeks, for example) or originate in the upland plateau to the south (Newaukum Creek). All the lowland tributaries have been affected by the agriculture use that has dominated the valley for over 100 years. Portions of these streams have been channelized, dredged, and re-directed along property lines and roadsides. Little of the native riparian habitat remains, even in the lower, wooded valley of Newaukum Creek. This reach remains forested but is dominated by deciduous trees that have colonized the cutover areas. Nevertheless, these streams are used by coho salmon and some steelhead, and many restoration actions are underway to regain lost habitat. In the lowermost reaches of the river, few streams remain above ground through the industrialized landscape. An exception is Hamm Creek, whose restoration became the personal crusade of one local resident for 20 years and has resulted in a much-restored stream amid the otherwise-industrialized landscape.

The mouth of the Green-Duwamish River empties into Elliott Bay via the heavy industrial area of Seattle that was once the estuary of the river. Little of the estuary remains—about 11 hectares (28 acres) in a single small area near Kellogg Island in the lowermost river. Recently, the US Army Corps of Engineers and King County have been cooperating in projects to regain some of the lost estuarine habitat.

White River

The White River is 122 kilometers (76 miles) long and has its headwaters on the northeastern slopes of Mt. Rainier from meltwater of the Emmons and Fryingpan glaciers. The river gets its name form the color of the glacial flour that is carried by the flow from its headwaters. The river flows through Pierce County for about 40 kilometers (25 miles) until the confluence with the Greenwater River. From this confluence downstream for approximately 51 kilometers (32 miles), the White River forms the southern boundary of King County. The uppermost reaches of the White River (in Pierce County) flow generally north through mountainous terrain, between steep, forested valley walls that rise quickly from the river’s edge to over 1,830 meters (6,000 feet). The upper gradient of the White River is precipitous, with many falls, cascades, and steep rapids, and a streambed composed of large boulder and bedrock. The major tributaries in this section are Huckleberry Creek, Silver Creek, and Fryingpan Creek. 

The gradient and terrain moderate somewhat near the community of Greenwater, where the White picks up the Greenwater River as a major tributary. From here, the river flows for about 35 kilometers (22 miles) west through an intermittently broad and narrow valley with steep, densely forested sideslopes. The stream bed maintains its mountain-like character throughout most of its length but some pool and riffle sections can be found where the valley broadens and the stream’s gradient lowers. Just upstream of the town of Buckley, near river kilometer 48 (river mile 30) and 74 kilometers (46 miles) from its headwaters, stands Mud Mountain Dam, a flood control dam completed in 1947 to control severe flooding in the lower Puyallup River valley. The river below the dam is a fast-flowing glacial stream with a boulder and rubble bed, and few areas are level enough to allow gravel accumulation. Five miles below the dam is a second structure, a diversion dam that for the past 100 years or so has shunted water off the river (to Lake Tapps, an artificially enlarged lake that is used as a reservoir) for power generation. For most of that time, the diversion reduced the flow dramatically in the 34 kilometers (21 miles) of the bypass reach. The diversion is no longer used to produce power; instead, some water is still diverted to maintain the artificial lake that is surrounded by residences and is used mainly for recreation. During the decades that flow was diverted for power production, the bypassed reach of the river often experienced flows that were a small percentage of the natural flow. In fact, a flow record from 1959 shows that the flow in one area of the bypass reach of the river reached almost zero during one diversion episode.

From the diversion dam downstream for about 19 kilometers (12 miles), the White River flows through a relatively confined valley averaging 1.6 kilometer (1 mile) in width with steep valley walls that rise abruptly to about 122 meters (400 feet). It remains turbid with glacial silts and is characterized by continuous braiding and channel splitting, an outcome of regular sediment flushes from Mud Mountain Dam and the variable flow regime imposed on the river. Negotiations are underway to address flow management issues in the hope of regaining some of the ecological function lost as a result of past river management.

At river kilometer 12.9 (river mile 8), the White River takes an abrupt turn to the south to follow the old Stuck River channel to its confluence with the Puyallup River. In 1914, a flood control project jointly carried out by King County and Pierce County diked off the White River channel and permanently redirected the flow of the White into the Stuck River and on into the Puyallup. In this lowermost reach, the White is completely diked and channelized to protect the adjacent farmland and industry from flood damage.

Despite the modifications, several species of salmon use the White River for spawning and rearing. A run of Spring Chinook , the only spring-type population this far south in Puget Sound, still uses the upper White and its tributaries—Huckleberry Creek, the West Fork White, the Clearwater River, and the Greenwater river—for spawning and rearing. These fish are trapped at a facility near the diversion dam and hauled above Mud Mountain Dam, where they are released to continue their migration. A separate population of fall Chinook uses much of the lower White River, despite the glacial flour that colors the water. Likewise, coho salmon use much of the lower White and its upper tributaries for spawning, but the numbers in the upper watershed are fairly low given the steep and swift character of the upper tributaries. Pink salmon (whose numbers have increased recently), chum salmon, and steelhead also use the lower White River for spawning.