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algae growth, freshwater lake


Lake Chelan is the longest (81 km) and deepest (>400 m) natural lake in Washington, formed by glacial retreat at the end of the last Ice Age. Based on water quality data collected in the 1980s, it is considered an oligotrophic lake (Rector and Hallock 1990) and has some of the clearest waters in the state. The Stehekin River is the primary tributary to the lake. Lake Chelan is used extensively for recreation and fisheries (Schoen and Beauchamp 2010). Lake Chelan’s water level is maintained by a dam operated by Chelan County PUD. Water withdrawals include municipal, drinking water, and irrigation uses. Development in the watershed is concentrated around the shallower Wapato Basin, consisting primarily of agriculture, cattle grazing, logging, and residences (Rector and Hallock 1990).

Given the lake’s importance for recreation and drinking water, there are concerns about the growth of algae in nearshore areas. One species of note is the invasive alga, Didymosphenia geminata (“Didymo”). Didymosphenia grows in low nutrient waters and has become established in rivers on most continents, and is widespread in western North America (Spaulding and Elwell 2007). Didymosphenia is a stalked diatom that can form thick mats and is considered a nuisance species. It is hypothesized that Didymosphenia spreads with human vectors (e.g., fishing equipment; Bothwell et al. 2009), though recent studies suggest that changing environmental conditions are also facilitating range expansion (e.g., Lavery et al. 2014). Didymosphenia has been found in a number of locations in Washington (Kumar et al. 2009), including the Chelan River. Regardless of the reasons for its range expansion, lake users should be aware of the presence of this invasive species and follow best practices to prevent the spread of this and other aquatic invasive species (e.g., Clean, Drain, Dry; Play, Clean, Go; WA Invasive Species Council 2021).




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