Mitigating aquatic invasive species impacts to Lake Chelan

Eurasian watermilfoil

Written by: Brian Patterson

Lake Chelan is Washington’s largest natural lake, and its watershed is an important tributary to the Columbia River. The lake is divided into two distinct basins – the upper Lucerne Basin with a maximum depth of 1,486 feet and the lower Wapato Basin with a maximum depth of 400 feet. These two basins are 38 and 12 miles long, respectively, for a total length of 50 miles.

Curly-leaf pondweed

curly-leaf pondweed

The lake is the treasure of the Lake Chelan Valley and has thus far remained in a relatively pristine state. However, like so many other lakes throughout the world, Lake Chelan is threatened by the proliferation of aquatic invasive species (AIS). AIS are introduced species that spread aggressively in lake, river, stream, and wetland ecosystems; displace native species and habitats; and/or alter aquatic ecosystem processes such as nutrient cycling. Because of their propensity to dominate shoreline habitats in lakes, aquatic invasive species are an immediate threat to the ecological, recreational, and aesthetic features of Lake Chelan.

Aquatic invasive species known to already inhabit Lake Chelan include Eurasian watermilfoil, curly-leaf pondweed, and freshwater clams. Eurasian watermilfoil and curly-leaf pondweed form thick mats in shallow areas of a lake, quickly growing and spreading to block sunlight, killing off native aquatic plants that fish and other underwater species rely on for food and shelter.

Quagga zebra mussels

Quagga zebra mussels

The extent of the existing habitat of these AIS are currently being studied (with an updated survey report published in 2022). Nearly 500 acres of Eurasian watermilfoil have been recently documented in Lake Chelan. Potential methods of removing/reducing Eurasian watermilfoil and curly-leaf pondweed being considered, including diver-assisted suction harvesting.

Of even greater concern is the potential for additional AIS to take hold in Lake Chelan such as zebra or quagga mussels, as these AIS can have devastating effects on the ecological balance of the lake and impact water intake systems, docks, and watercraft. If zebra and/or quagga mussels were to become established in Lake Chelan, the ecological and economic impacts would be staggering.


Chelan Basin Conservancy is partnering with other local groups (such as Keep It Blue Lake Chelan and the Lake Chelan Research Institute) to study and combat the proliferation of AIS in Lake Chelan. Reducing and preventing AIS in Lake Chelan requires a combination of public education and the development of new programs. Mitigating the spread of AIS often focuses on keeping watercraft from being carriers from one water body to another. As such, one likely outcome of the fight to prevent the introduction new AIS, and the expansion of existing AIS, will be to develop a boat inspection program for Lake Chelan.

Chelan Basin Conservancy is proud to be working alongside other groups and agencies dedicated to increasing awareness and educating residents and visitors to the lake about valuable steps they can take to help protect Lake Chelan.

Additional Resources:

Visit Keep it Blue Lake Chelan to learn what you can do to help.

Lake Chelan Research Institute – Learn more about the current environmental conditions in Lake Chelan:

Chelan County Web Page – Lake Chelan Watershed Planning Unit:

Lake Chelan Vulnerability and Habitat Suitability Analysis for Aquatic Invasive Species Report:

Chelan County Web Page – Lake Chelan Water Quality:

Washington Department of Fish and Wildlife

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Chelan Basin Conservancy
PO Box 1073
Chelan WA 98816

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