Freshwater Exotic and Invasive Plants


Elodea spp., within the Hydrocharitaceae or waterleaf family, is the only known exotic, invasive submerged freshwater plant to occur in Alaska.  First reported in 1982 in Eyak Lake near Cordova, it was subsequently found in Chena Slough near Fairbanks in 2009 and in Sand Lake in Anchorage in 2010.  In September 2012, it was identified in Stormy Lake on the Kenai National Wildlife Refuge while that lake was being treated with rotenone in an effort to eradicate introduced northern pike.  It was subsequently found in Daniels Lake in October 2012, Beck Lake in 2013, and Hilda-Seppu and Sports Lakes in 2017. Genetic analysis of specimens from Stormy and Daniels Lakes indicate that it is a hybrid, Elodea canadensis X nuttalli.

Elodea is a particularly injurious aquatic perennial. Outside its native range in North America, and elsewhere in Europe, New Zealand, Australia, and Africa, it has compromised water quality, grown so abundantly that boat traffic is hindered, reduced dissolved oxygen, and severely impacted native fisheries. A recent bioeconomic risk analysis suggests that Elodea is likely to cost Alaska $97 million per year in lost opportunities for commercial sockeye fisheries and recreational floatplane pilots (Schwoerer 2017).

Elodea is also insidious, in that only a plant fragment is needed to infest a water body because it reproduces vegetatively. Likely initial vectors on the Kenai Peninsula and elsewhere in Alaska were dumped aquaria and discarded commercial lab kits. However, as these early populations of elodea become better established, motor boats, anchors, fishing gear, float planes and even waterfowl will become the greater risk.  So early detection and eradication of Elodea is critical if other waterbodies on the Kenai Peninsula are to remain free of Elodea.  Over 100 at-risk lakes on the Kenai Peninsula have already been surveyed for Elodea.

Refuge biologists, cooperating with many partners of the Kenai Peninsula Cooperative Weed Management Area, are actively working to eradicate Elodea from the Kenai Peninsula.  After developing an Integrated Pest Management Plan, fluridone (Sonar Genesis®, SonarONE®) and diquat (Reward®, Littora®) were used to treat Beck, Daniels and Stormy Lakes in 2014-2015; elodea has not been detected in these three lakes since September 2015.  Hilda-Seppu and Sports Lakes were treated in 2017 and appear to be eradicated as of September 2019.  Unfortunately, a sixth elodea infestation was found in Sandpiper Lake in September 2019, but plans are already underway for treatment in early 2020.  In short, five of six infestations have been successfully eradicated from the Kenai Peninsula.  Combined with outreach, institutional/agency support, and monitoring for early detection of novel infestations, it may be possible to keep elodea at bay on the Kenai Peninsula.  Refuge biologists continue to work with organizations in other parts of the state to eliminate this plant from Alaska.