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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.  A survey of 68 lakes on the Kenai Peninsula during summer 2013 revealed that elodea populations are, in fact, constrained to three lakes (Stormy, Beck and Daniels Lakes) in two coastal watersheds north of Nikiski. Genetic analysis of specimens from these three lakes indicates that it is a hybrid, Elodea canadensis X nuttalli.

Five distinct species of elodea are recognized, all native to the New World. Elodea canadensis or Canadian waterweed is native to temperate North America, originally distributed primarily in the Great Lakes region. The native range of E. nuttallii (Nuttall’s waterweed) tends to overlap with E. canadensis, but the former is more prevalent further south.  Elodea bifoliata occurs primarily in temperate western North America.  Elodea potamogeton and E. callitrichoides are both native to South America.

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. Elodea is 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 are 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 the sooner Elodea is eradicated from these three lakes, the more likely it is that other waterbodies on the Kenai Peninsula will remain free of elodea.

Refuge biologists, cooperating with many partners of the Kenai Peninsula Cooperative Weed Management Area, are actively working to eradicate elodea, contingent on funding.  An Integrated Pest Management Plan calls for four applications of fluridone, a selective systemic herbicide, over three years (2014-16).  Combined with outreach, institutional/agency support, and monitoring for both efficacy (short term) and early detection of novel infestations (long term), it may be possible to eradicate existing elodea populations from, and to keep new infestations off, the Kenai Peninsula.

Last Updated: Apr 20, 2015
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