page_title: Puyallup River
section_title: River modifications
hierarchical_section_title: Puyallup River / River modifications
caption_attribution_description: English: The McMillin Bridge over the Puyallup River in McMillin, Washington, USA.
context_page_description: The Puyallup River is a river in the U.S. state of Washington. About 45 miles long, it is formed by glaciers on the west side of Mount Rainier. It flows generally northwest, emptying into Commencement Bay, part of Puget Sound. The river and its tributaries drain an area of about 948 square miles in Pierce County and southern King County.
  The river's watershed is the youngest in the Puget Sound region, having been formed from a series of lahars starting about 5,600 years ago. The valley's 150,000 residents are at risk from future lahars. For this reason, the United States Geological Survey has installed a lahar warning system.
context_section_description: The Puyallup River and its main tributary, the White River, have been subjected to major modifications during the 20th century. The Puyallup River between Sumner and its mouth at Tacoma was straightened. A diversion dam was built at Game Farm Park in 1914 to prevent the White River from flowing on its natural course into the Green River at Auburn; since then it has flowed into the Puyallup River instead of the Green River. Flood protection structures were built along many rivers in the basin, including extensive levees. A flood storage reservoir, Mud Mountain Lake, was created on the White River with the construction of Mud Mountain Dam. As part of the flood control efforts, river channels and embankments have been generally kept clear of debris such as gravel bars, large trees, logjams, and other woody debris. These modifications have radically altered the natural character of the rivers. River widths have been generally reduced. Water now fills nearly all of the land between river banks, instead of the historic pattern of braided meanders and wetlands.
caption: Bridge across the river at McMillin, Washington
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