A survey of aquatic invasive species conducted in Lake Chelan in August and September of 2021 shows that invasive aquatic plants are more widely distributed in the Wapato Basin and lower Lucerne Basin of the lake compared to survey results from eight years ago.

The survey covered the entirety of the Lake Chelan shoreline and mapped 520 acres of invasive aquatic plants, predominantly Eurasian Water Milfoil and Curly Leaf Pondweed. The survey also documented an increase in the northern extent of aquatic invasive plants within the lake including shoreline locations frequently used by boaters.

Most of the invasive aquatic plants were identified near developed and shallow shorelines in the southern basin of the lake. The survey also found that invasive aquatic plants also spread up lake to other high-use areas. These new observations unfortunately confirm the continued spread of invasive aquatic plant species within Lake Chelan.

The research not only documented extensive invasive aquatic plants in Lake Chelan but also included a limited survey of invasive freshwater clams (Corbicula fluminea). Invasive freshwater clams were observed at several locations during the survey. Invasive clams are a concern because they have the potential to influence water quality and impact native species. Anecdotal observations by Lake Chelan Research Institute and local fishing guides suggest that freshwater clams are increasing in Lake Chelan and that they serve as a food source for lake trout. Additional study is needed to determine their extent, importance to fish, and impact on Lake Chelan water quality.

The survey results indicate the need to actively control invasive aquatic plants and possibly freshwater clams in Lake Chelan. Results also demonstrate the importance of Chelan County PUD’s lowering of the lake level during fall and winter months. The extent of invasive aquatic plants would be worse than it is currently if the lake level was not lowered annually.

The Aquatic Invasive Species Survey was made possible by private donations to the Lake Chelan Research Institute ($25,000.00) and the Chelan County PUD ($5,000.00). Four Peaks Environmental Science and Data Solutions of Wenatchee conducted the survey under contract to the Lake Chelan Research Institute and in collaboration with the Chelan County Natural Resources Department, the Chelan County Noxious Weed Control Board and the Chelan County PUD.