Вашингтон штатының Капитолий жанындағы жасалма көл

Artificially created body of water at Washington State Capitol

Capitol Lake is a 3 kilometer (1.9 mile) long, artificial lake at the mouth of Deschutes River in Tumwater/Olympia, Washington. The Olympia Brewery sits on Capitol Lake in Tumwater, just downstream from where the Tumwater Falls meet the artificial lake. The Washington State Department of Enterprise Services (DES) manages the lake, as part of The Washington State Capitol Campus.

Prior to American settlement, the tidal basin at the southern tip of Budd Inlet was a productive shellfish gathering area for native peoples. The area was of specific value to the Squaxin Island Tribe who inhabited the original estuary for millennium. In 1911, the State Capitol Commission held a nationwide competition for the design of the State Capitol Campus. The winning architects, Wilder and White, submitted a revolutionary City Beautiful movement and American Renaissance plan which included creating a body of water to reflect the Capitol Group of buildings on the bluff by installing a tidelock at the mouth of the Deschutes River. A more limited lake was also part of the original landscape design by John Olmsted to reflect the Washington State Capitol building on Puget Sound. The lake as envisioned by Olmsted would have been created with a north to south running berm, as opposed to an east to west running dam. In 1915, the State Capitol Commission rejected a plan by former Olympia Mayor and state legislator P. H. Carlyon to replace Olympia's bridge to the westside with a dam and locks. That plan would have created a lake very much like the present Capitol Lake. Because of opposition from upriver Tumwater businesses, such as the Olympia Brewing Company and the Olympia Power and Light Company, that plan was not approved. The Capitol Group of buildings was constructed over several years from 1913 to 1940, and the State Capitol Committee then turned to the task of creating the Wilder and White reflecting Capitol Lake. In 1937, the state began purchasing the privately owned tidelands around the Capitol Campus. In 1941, opposition from Tumwater was finally overcome during a special town meeting. Capitol Lake was created in 1951 when the dam, known as the Fifth Avenue Dam, was completed consistent with the Wilder and White plan. This allowed for the retention of the outflow from the Deschutes River to cover the tide flats. Due to an increase in bacterial levels, swimming in the lake was banned beginning in the 1980s.

As Capitol Lake replaced the Deschutes River estuary the area underwent a high rate of siltation. The lake was dredged periodically to keep it from filling in, potentially offsetting eutrophication. Along with sediment issues and an introduction of an invasive species, poor water quality became an issue due to bacterial levels, causing the lake to be closed to swimmers for several decades. After a 25 year hiatus, in 2011 the State Legislature appropriated $200,000 in order to seek permits to reimplement maintenance dredging in order to retain and improve Capitol Lake as part of the historic Wilder and White design of the State Capitol Campus during its centennial year. The Washington State Department of Ecology released a report in 2012 that studied several areas of concern for the Deschutes River, Capitol Lake, and Budd Inlet, including bacterial and oxygen levels, sediment, and temperature. A 2022 report noted an accumulation of an additional 35,000 cubic yards of sediment per year. A heavy cold snap in 2013, combined with a drawdown in water level in preparation, was roughly estimated to have killed 40–60% of the mudsnail population. An infestation of Eurasian milfoil was controlled using herbicide in 2004. Later efforts relied on scuba divers to remove this invasive plant.

Capital Lakefair, centered on the lake, is held annually in July. The trail around the lake is 1.5 miles long. as of 2023, no boating or swimming activities are allowed within the lake.