Document Type

Technical Report

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Aquatic plants, Lake Roosevelt National Recreation Area (Wash.), Invasive plants


Lake Roosevelt is a large reservoir in northeast Washington State formed by the Grand Coulee Dam. The reservoir, which inundates portions of the Columbia River, the Spokane River, and other rivers and streams, is the focus of the Lake Roosevelt National Recreation Area (LARO) that is managed by the National Park Service. LARO encompasses 100,390 acres (40,625 ha) and includes significant cultural and recreational resources. The surface area, volume, and shoreline length of Lake Roosevelt at full pool is 82,691 acres (33,490 ha), 9.41 × 1010 acre-ft (1.16 × 1010 m3) (Nigro et. al. 1981), and 630 miles (1014 km) ( accessed 28 January 2008), respectively; thus, the reservoir provides a significant aquatic resource for fish and wildlife as well as recreation in the region.

Invasive plants are a high-priority “vital sign” of LARO ecosystem health (Garret et. al. 2007). In recent years, LARO staff noted an increase in the density of submersed aquatic plants (macrophytes), including Myriophyllum spicatum (Eurasian watermilfoil), in the lake. M. spicatum is a highly invasive weed that forms dense surface mats that interfere with boating and angling and degrade water quality. In an effort to reduce recreational impacts of aquatic plants LARO staff established test plots of nonchemical methods of control during the drawdown period in the spring of 2007.

The National Park Service contracted Portland State University Center for Lakes and Reservoirs to accomplish two main objectives: 1) document the effects of nonchemical control measures of submersed aquatic plants in the reservoir, and 2) describe the composition of the aquatic plant community at selected locations in LARO.


Natural Resource Report NPS/MWR/HTLN/NRTR—2008/076

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