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Aquarium plant threatens Peninsula waterways

Posted: September 13, 2012 - 3:58pm  |  Updated: September 14, 2012 - 9:39am
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Photo by E. Bella, Kenai National Wildlife Refuge How Elodea moves from lake to lake: we don't want to see this when our boats are trailered!
Photo by E. Bella, Kenai National Wildlife Refuge How Elodea moves from lake to lake: we don't want to see this when our boats are trailered!

Interagency biologists working on northern pike control last week in Captain Cook State Recreation Area noticed fragments of a bright green, whorled-leaf aquatic plant washed up on the shore near a boat launch. This unusual plant was identified as a species of Elodea, likely Elodea canadensis, the Canadian waterweed. Elodea is known from several locations in Alaska including Fairbanks, Anchorage, and Cordova…and now Stormy Lake on the Kenai Peninsula. This is the first aquatic freshwater invasive plant species that has been confirmed in Alaska.

This perennial plant is native to much of North America south of mid-BC, Canada, and has naturalized in many places in the British Isles, where it is a problem. Canadian waterweed is closely related to western waterweed (Elodea nuttallii), a native of both North America and Eurasia. In Europe, western waterweed is more common, as it is thought to compete better through faster nutrient uptake. The two hybridize and are virtually impossible to tell apart unless you can find a rare flowering stalk.

So what’s the big deal? Effects of Elodea infestations are severe. Its growth can be thick enough to choke and damage boat motors and prevent any kind of recreational use. Forget swimming or paddling around an Elodea-clogged lake – unless you like the feel of the Creature from the Black Lagoon grabbing your legs. Ecological effects include lower water quality, increased sedimentation, native vegetation displacement, and most seriously – which gets the attention of many residents – degraded salmon spawning habitat.

How did Elodea get here? There are several theories, but the prevailing one is that because it’s a common aquarium plant, all the Alaska populations are the result of single or multiple aquarium dumps into our water systems. Elodea is sold in most pet stores and aquarium supply shops in Alaska and across North America. It has also been used in science kits for high school science labs to study plant carbon dioxide use. The plant may be spread by migrating waterfowl, but this is mostly speculative.

Alaska and the Kenai Peninsula already have a number of non-native plant species found across the landscape – so why worry about yet another invasive plant? Elodea may be especially difficult to control and particularly damaging because of three factors: the way the plant reproduces, the way it can be spread around Alaska, and the plant’s habitat preference.

Elodea reproduces asexually from plant parts. In the fall, leafy stalks detach from a parent plant, float away, root, and start new plants. Winter buds grow from stem tips that overwinter in the water body’s bottom. The plant is brittle and breaks apart when agitated, making it very difficult to chop up and remove without causing a major influx of reproductive-ready vegetative parts into the already-infected system. Flowering is rare in all Elodea species, with reproduction by seed virtually nonexistent.

A huge concern is how easily fragments of Elodea can be picked up by float planes and boats. Boat motors can fragment and chop the plant into smaller pieces, making it spread and reproduce faster. Sand Lake is very close to Lake Hood, the major float plane base in Anchorage – close enough to visualize how fast plant parts could be spread all over the state from this single source. Boat motors and other gear also readily pick up fragments of the plant and can spread it to nearby rivers and lakes where the reproduction pattern starts all over again.

Elodea prefers a cold, slowly-flowing (less than one meter per second) water system, with clear water and silty or organic substrate to root in. It can stand freezing and temperatures up to around 80F. In other words, Elodea is ideally suited to thrive in most of the wetland, pond, and slow-moving rivers systems of the western Kenai Peninsula and other big chunks of the state.

While we don’t know all the potential spread avenues, we do know that most Alaskan water systems will be losers in an Elodea invasion. Biologists around the state are alarmed enough that a subgroup of our statewide invasion group (CNIPM) teleconferences regularly to discuss updates and options concerning the Elodea invasions.

What can we do to stop the spread of Elodea and other aquatic invaders? There are a number of ways to sanitize gear between trips or between waterways to prevent introduction into uninfected waterways. Wash all gear carefully to remove any mud, plant parts, and debris before leaving the boat launch or fishing spot. Later, you can dry the gear, freeze gear solid, or wash in water over 130F. If these steps aren’t possible, blast gear using a 2 percent bleach solution to kill anything living on it. The strongest tool in our invasion toolbox for aquatic invaders, however, is prevention – keeping Elodea out of our ponds and waterways before it becomes a problem.


Dr. Elizabeth (“Libby”) Bella is an ecologist at Kenai National Wildlife Refuge. You can find more information about the Refuge at or

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