Environmental Factors

Spotted Knapweed
Spotted Knapweed is a common invasive plant species around Lake Roosevelt. Click the image to see more invasive plants.

Lake Roosevelt National Recreation Area was created to provide visitors excellent recreational opportunities while preserving the area's natural and cultural resources. This goal can be difficult because of the special environmental factors encountered at Lake Roosevelt. The natural resources of the area are subject to a range of threats, including exotic species, pollution, and changing lake levels.

Exotic Species

Plants are everywhere we live, work, and recreate. Plants tell a story of adaptation stemming from environmental stressors to human occupations that act as a road map to understand population density and dispersal. Lake Roosevelt National Recreation Area is located in a semi-arid transition zone, plant communities along the 150 mile-long reservoir gradually change from shrub steppe plant communities to ponderosa pine forest. The actual reservoir has its own unique aquatic plant species in addition to riparian vegetation along its margins.

Although Lake Roosevelt has three distinct plant communities, the last 100 years of human occupation has added too, and in some case replaced portions of these plant communities. Replaced with what? - Invasive species. Invasive species are defined as a species that is non-native (or alien) to the ecosystem and whose introduction causes or is likely to cause economic or environmental harm or harm to human health. In some cases this was done purely by accident, the most common is the spread of invasive plants along transportation thoroughfares such as roadway and bodies of water.

Lake Roosevelt is not immune to invasive species; a preliminary survey of 1,233 terrestrial park acres (10% of the parkland) identified 181 acres of 12 different invasive plant species. The most common invasive plants identified in the upland areas were: Spotted knapweed, Rush skeletonweed, Dalmation toadflax and Leafy spurge.

The lake or aquatic environment is no different. Several non-native species thrive in the shallow littoral zones and riparian margins. The most common aquatic invasive plant identified in the lake was: Eurasian watermilfoil.

What can you do to prevent the spread of invasive plant species?

1) Drive only on established roads and trails away from weed infested areas.

2) When using pack animals carry only feed that is certified as weed-free.

3) Know what you are planting and the potential strategies for escape to natural areas.

4) Remove seeds from vehicle tire tread and clothing.

5) Avoid driving recreation vessels through watermilfoil mats.

6) Prevent the spread of Eurasian watermilfoil by removing plant fragments from boat props, trailers, fishing lines, etc….

Lake Roosevelt is striving to identify invasive weed population within the recreation areas boundaries. Please contact us if you find invasive plant populations or have question or concerns about invasive plants.


In the early 1980s, concerns about water quality in Lake Roosevelt were first reported in a U.S. Fish and Wildlife study that reported elevated concentrations of arsenic, cadmium, lead, and zinc in fish. Follow-up studies identified the primary source of the contamination to be a lead-zinc smelter owned by Teck Cominco, a Canadian company with U.S. subsidiaries, on the Columbia River in British Columbia just upstream from the international boundary. Since the 1950s, the smelter had discharged several hundred tons of furnace slag and effluent per day into the Columbia River.

In June 2006, EPA released beach sediment data from samples that were collected from 15 beaches at Lake Roosevelt. In the spring of 2005, nine developed beaches within the recreation area were sampled, three beaches on the Colville and Spokane Reservations were sampled, and three beaches north of the recreation area were sampled.

All 15 samples taken within the recreation area and reservations tested within acceptable health based risk standards for short-term recreational users (i.e. 14 consecutive days on one beach in the summer). The three beaches north of the recreation area had slightly elevated levels of arsenic and one of those beaches had slightly elevated levels of lead. These three beaches will be further evaluated by EPA as their study of the Upper Columbia progresses.

Fish tissue analysis is ongoing and initial results expected be released in the summer of 2007.

Changing Lake Levels

Another challenge to managing the recreation area is the constantly fluctuating water levels. This constant shift between lake and dry land makes the preservation of natural and cultural resources difficult. The lake level varies depending on inflow from rain and snow pack and outflow from the dam. The elevation of the surface of Lake Roosevelt is measured from sea level. An elevation of 1290’ is considered “full pool,” however fluctuating water levels have gone as low as 1208’. Low lake levels leave boat ramps high and dry, and also expose a great deal of previously inundated land.

A host of native plants colonize the riparian areas along the lake. The area around 1290’ is dominated by Phalaris arundinaceae (reed canarygrass). It occupies most of the area within a few feet in elevation of the annual high water line. There are extensive stands of this grass in large shallow bays (ex. near Kettle Falls Campground) and shoreline marshes (Ex. down from Napoleon Bridge). Other less abundant species occupy this zone as well, Coreopsis atkinsonii (Tickseed), Carex lenticularis (Sedge), Alopecuris aequalis (Shortawn foxtail) have been found and other species would be expected to be found by a more thorough survey.

In the areas that are submerged for the majority of the summer aquatic plants are dominant. These plants are generally less course than the grasses and sedges at the full pool level and therefore may be more heavily grazed by waterfowl. Various species of pondweed (Potamogeton) are abundant, with Eurasian water milfoil (Miriophyllum aquaticum) common in certain areas. During the spring drawdown, various annuals can be found among the pondweed on the exposed lakebed. Plagiobothrys (Popcornflower) and diminutive annuals in the mustard family have been observed but not positively identified.

Eurasian Watermilfoil
Eurasian Watermilfoil is one of the most invasive
under water plant species.

Last updated: February 28, 2015

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Mailing Address:

Lake Roosevelt National Recreation Area
1008 Crest Drive

Coulee Dam, WA 99116



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