| Lake Washington | |
|---|---|
| x̌ačuʔ (Lushootseed) | |
.jpg) The two longest floating bridges in the world cross Lake Washington | |
 Show Lake Washington Show King County Show Washington Show the United States | |
| Location | King County,Washington, United States |
| Coordinates | 47°37′N122°16′W / 47.617°N 122.267°W /47.617; -122.267 (Lake Washington) |
| Primary inflows | Sammamish,Cedar Rivers;Ravenna,Thornton,Kelsey,Juanita,Forbes andCoal Creeks |
| Primary outflows | Lake Washington Ship Canal (1916) |
| Catchment area | 315,000 acres (1,270 km2) |
| Basin countries | United States |
| Max. length | 22 mi (35 km) |
| Surface area | 33.8 square miles (88 km2), 33.8 square miles (21,600 acres) |
| Average depth | 108 ft (33 m) |
| Max. depth | 214 ft (65 m) |
| Water volume | 2,350,000 acre⋅ft (2.90 km3) |
| Surface elevation | 16 ft (4.9 m) above mean sea level, 20.6 ft (6.3 m) above Puget Sound mean lower low tide |
| Islands | Mercer Island,Foster Island,Bird Island (Washington),[1] Marsh Island
|
| References | King County[2] |
Lake Washington (Lushootseed:x̌ačuʔ)[3][a] is a large freshwaterlake adjacent to the city ofSeattle, Washington, United States.[4] It is the largest lake inKing County and the second largest natural lake in the state ofWashington, afterLake Chelan. It borders the cities of Seattle on the west,Bellevue andKirkland on the east,Renton on the south, andKenmore on the north, and enclosesMercer Island. The lake is fed by theSammamish River at its north end and theCedar River at its south.
Lake Washington has been known to theDuwamish and otherIndigenous peoples living on the lake for millennia asx̌ačuʔ (lit. "lake" inLushootseed).[3] At the time of European settlement, it was recorded as At-sar-kal in a map sketched by engineerAbiel W. Tinkham;[4]: 10 and theChinook Jargon name,Hyas Chuck ("great/large water"), was also used.[5] Other English names historically used for the lake include Lake Geneva byIsaac N. Ebey;[4]: 140 and Lake Duwamish in railroad surveys under GovernorIsaac Stevens.[4]: 174 Lake Washington received its present name in 1854 afterThomas Mercer suggested it be named afterGeorge Washington, as the newWashington Territory had been named the year before.
The lake provides boating and sport fishing opportunities. Some fish species found in its waters includesockeye salmon,coho salmon,Chinook salmon,rainbow trout,largemouth bass,smallmouth bass,yellow perch, andblack crappie.[6]
Lake Washington has two passengerseaplane bases:Kenmore Air Harbor on its north end; andWill Rogers – Wiley Post Memorial Seaplane Base on its south end, adjacent toRenton Municipal Airport.
Lake Washington's basin was formed by glacial processes associated with the Puget lobe of theCordilleran Ice Sheet during theVashon Glaciation, likely through a combination of preferential erosion of weak rock and sediments by the glacier itself and bysubglacial meltwater during the glacier's retreat. At the end of thePleistocene, the basin that is now Lake Washington connected directly to the channels ofPuget Sound through the north end of the Duwamish Valley.[7] The basin may or may not have been a waterway at this point, aseustatic sea levels were approximately 150 meters (490 feet) lower than at present[8] and the land around Seattle was about 75–85 meters (246–279 ft) lower due toisostatic depression from the weight of the glacier.[9] However, the rapid sea level rise from the end of thePleistocene through the earlyHolocene had flooded the Duwamish Valley and Lake Washington within a couple thousand years. Lake Washington did not become a freshwater lake, isolated from Puget Sound, until some time after 5,700 yearsBefore Present, when sedimentation in the Duwamish Valley closed off its southern end.[7] The new lake, lacking any other outlets, drained south through theBlack River into the Duwamish Valley and, ultimately, Puget Sound until the construction of theLake Washington Ship Canal in 1916.[10]
The main inflowing rivers are theSammamish andCedar Rivers, with the Cedar supplying most of the water. Seasonal changes in the flow of the Sammamish are moderated by aweir at the Lake Sammamish inlet.[11]
The lake is drained by theLake Washington Ship Canal.
In addition, there are numerous small creeks and rivers which feed the lake, including:[12]
Historically, construction of the Lake Washington Ship Canal drastically changed the inflow and outflow of the lake. Before construction of the canal in 1916, Lake Washington's outlet was theBlack River, which joined theDuwamish River and emptied intoElliott Bay. When the canal was opened the level of the lake dropped nearly nine feet (2.7 m).[13] The canal became the lake's sole outlet, causing the Black River to dry up and disappear. Before construction, the Sammamish River was the primary source of water for Lake Washington, and the lowering of the lake slightly increased its flow. As part of the ship canal project, the Cedar River was diverted into Lake Washington to become the lake's primary source.
TheMontlake Cut, part of theLake Washington Ship Canal, connects the lake toLake Union and ultimatelyPuget Sound.
Three concrete floating bridges cross Lake Washington:Evergreen Point Floating Bridge (SR 520),Lacey V. Murrow Memorial Bridge (I-90 eastbound), andHomer M. Hadley Memorial Bridge (I-90 westbound). The floating design is because Lake Washington's depth and muddy bottom prevented the emplacement of the pilings or towers necessary for the construction of acauseway orsuspension bridge. The bridges consist of hollow concrete pontoons that float atop the lake, anchored with cables to each other and to weights on the lake bottom. The roadway is constructed atop these concrete pontoons. Additionally, theEast Channel Bridge carriesInterstate 90 from Mercer Island toBellevue.
TheEvergreen Point Floating Bridge (officially the SR 520Albert D. Rosellini Evergreen Point Floating Bridge) carriesState Route 520 from Seattle'sMontlake neighborhood toMedina. The bridge opened in April 2016 and replaced the original Evergreen Point Floating Bridge at the site, which opened in 1963. The 7,710-foot-long (2,350 m) floating span is the longest floating bridge in the world, as well as the world's widest measuring 116 feet (35 m) at its midpoint.
TheLacey V. Murrow Memorial Bridge carriesInterstate 90 eastbound from Seattle'sMount Baker neighborhood toMercer Island. Originally opened in 1940, a portion of the Lacey V. Murrow Bridge sank during a windstorm on November 25, 1990. At the time, the bridge was closed for renovations. A Washington State Department of Transportation (WSDOT) investigation revealed that the incident resulted from the improper handling ofhydrodemolition water being used during the renovation, rather than in any basic flaw in the bridge's concept or design.[14] The bridge was subsequently rebuilt and reopened in 1993. The Murrow Bridge is the second-longest floating bridge in the world, at 6,620 ft (2,020 m).
TheThird Lake Washington Bridge (officially the Homer M. Hadley Memorial Bridge) carries the westbound lanes ofInterstate 90 and two tracks ofSound Transit's2 Line betweenMercer Island andSeattle. The first pontoon for the new bridge was floated in September 1983, and opened in June 1989. The floating bridge is the fifth-longest of its kind in the world, at 5,811 feet (1,772 m).
Steamboats and ferries operated on the lake from about 1875 to 1951. In 1892,John L. Anderson started to ferry betweenLeschi Park andNewcastle on the steamerWinnifred.Winnifred burned in 1894, but Anderson soon launched a fleet of several ships operated by theAnderson Steamboat Company. In 1913, the Port Commission of Seattle launched the steel-hulled steam ferryLeschi, undercutting Anderson's operations and he eventually went out of business in 1917. The public ferries continued operations until 1950, approximately one year after thetolls were removed from the Murrow bridge.[15]
The cities and towns bordering the lake, going clockwise from the west, areSeattle,Lake Forest Park,Kenmore,Kirkland,Yarrow Point,Hunts Point,Medina,Bellevue,Beaux Arts Village, andRenton. The city ofMercer Island occupies the island of the same name, in the southern half of the lake.
Around 1900, Seattle began discharging sewage into Lake Washington. During the 1940s and 1950s, eleven sewage treatment plants were sending state-of-the-art treated water into the lake at a rate of 20 million gallons per day. At the same time, phosphate-based detergents came into wide use. The lake responded to the massive input of nutrients by developing unpleasant blooms of noxious blue-green algae (cyanobacteria). The water lost its clarity, the desirable fish populations declined, and masses of dead algae accumulated on the shores of the lake. After significant pollution, the October 5, 1963 issue of thePost Intelligencer referred to the lake as "Lake Stinko". Citizen concern led to the creation of a system that diverted the treatment-plant effluents into nearbyPuget Sound, where tidal flushing would mix them with open-ocean water.
The diversion was completed in 1968, and the lake responded quickly. The algal blooms diminished, the water regained its clarity, and by 1975, recovery was complete. Careful studies by a group oflimnologists from theUniversity of Washington showed thatphosphate was the culprit. Since then, Lake Washington has undergone major improvements, drastically improving the ecology and water quality, making the water twice as clear as it was in 1950.[16]
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