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The Elwha Ecosystem Restoration Project is a 21st-century project of the U.S. National Park Service to remove two dams on the Elwha River on the Olympic Peninsula in Washington state, and restore the river to a natural state. It is the largest dam removal project in history and the second largest ecosystem restoration project in the history of the National Park Service, after the Restoration of the Everglades. The controversial project, costing about $351.4 million,〔 has been contested and periodically blocked for decades. It has been supported by a major collaboration among the Lower Elwha Klallam Tribe, and federal and state agencies. The removal of the first of the two dams, the Elwha Dam, began in September 2011 and was completed ahead of schedule in March 2012. Removal of the second dam, the Glines Canyon Dam, was completed on August 26, 2014. ==History of the Elwha River== Historically, the Elwha River was one of the few rivers in the contiguous United States that supported all of the anadromous salmonid species native to the Pacific Northwest.〔(【引用サイトリンク】title= Restoration of the Elwha River Ecosystem )〕 Ten stocks of anadromous salmon and trout species are known to have been present in the river before the dams were built: spring- and summer/fall-run Chinook salmon (''Oncorhynchus tshawytscha''), chum salmon (''O. keta''), coho salmon (''O. kisutch''), pink salmon (''O. gorbuscha''), sockeye salmon (''O. nerka''), summer- and winter-run steelhead trout (''O. mykiss''), bull trout (''Salvelinus confluentus''), and cutthroat trout (''O. clarki clarki'').〔(【引用サイトリンク】title= Elwha river Salmonid Assessment: Adult Weir Project. 2010 ANNUAL REPORT )〕 The river was considered the most prolific fish producer on the Olympic Peninsula. It was particularly known for its very large Chinook salmon, weighing as much as .〔 Prior to the construction of the two dams on the river in the early 20th century, an estimated 392,000 fish returned annually to spawn. By the late 20th century, the number had declined to less than 3,000.〔 Pink salmon were historically the most numerous salmon species in the river, with over 250,000 adult returns. By the 1980s that number fell to near zero.〔(【引用サイトリンク】title= Freeing the Elwha )〕 Coho occupied the largest area of the watershed, going up many of the tributaries, and nearly to the headwaters of the Elwha River. Salmon were long an extremely important food source for the Lower Elwha Klallam people. They have occupied territory in this area for thousands of years, and still live on land at the mouth of the river.〔(【引用サイトリンク】title= Elwha River Restoration: Background and History )〕 The salmon runs provided a valuable food source for many animals, such as black bear, coyotes, gray wolves, bald eagles, raccoons, and dozens of others. In addition, salmon carcasses littered stream banks during prime fall and spring spawning, providing food for scavengers and decaying and enriching the soil. In the Elwha River basin, salmon once contributed over 300 tons of phosphorus and nitrogen every year, via decaying carcasses and the scat of predators and scavengers. In this way salmon played an important role in the overall health of the ecosystem. About 130 species benefit from the nutrients in salmon carcasses. Today, about 83% of the Elwha River's watershed lies within Olympic National Park, where it is protected, more than that of any other river on the Olympic Peninsula. Most of the Elwha's basin is in pristine condition, unlike many other rivers on the peninsula whose basins have been harmed by extensive land use, especially logging. Above the dams, the Elwha's basin remains largely in a natural condition. Limited development has occurred downriver from the park boundary. Water is withdrawn for municipal and industrial use and there is some logging.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Elwha Ecosystem Restoration」の詳細全文を読む スポンサード リンク
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