Keeping Elodea Out of Alaska's Salmon Lakes: An Invasive Waterweed and the Parks' Response

Alaska has one of the most productive salmon fisheries in the world, and an invasive plant threatens the lakes where salmon spawn. Money from the Bipartisan Infrastructure Law (BIL) has given new energy to early detection: finding Elodea and keeping it out of freshwater salmon habitat.

Salmon spawning in Tazimina Lake, Lake Clark National Park and Preserve. NPS / Dan Young.

What Elodea is

Elodea is a genus of waterweeds — highly invasive aquatic plants. They spread easily between waterbodies and, once established, are very hard to eradicate. Elodea was the first freshwater invasive plant known in Alaska.

• How it spreads: small fragments ride on boots, boats and float planes that have been in infested water.
• What it does: an established bed grows fast, blocks light and takes up nutrients. It clogs waterways and changes the physical structure of salmon habitat — salmon lay their eggs on rocky stream and lake bottoms.

A recent study linked Elodea to harm to salmon: widespread Elodea may change habitat in ways that affect fish growth, and could affect whole populations by keeping salmon from returning to the waters where they were born to spawn.

Elodea grows thick and changes the structure of fish habitat. U.S. Fish and Wildlife Service.

The risk to the parks

Elodea has not yet been found in Alaska's national parks, but it is known in waterways used to reach them. Most of these high-risk places can be reached only by float plane or boat — the main ways Elodea travels.

Tobias Schwoerer, an assistant research professor of natural resource economics at the University of Alaska Fairbanks, says early detection must grow a great deal: current risk assessments cover only about 700 of the more than 200,000 lakes float planes use in Alaska.

With BIL funds, the National Park Service will survey high-risk rivers and lakes for Elodea and treat infested waters nearby to remove it.

Why it matters

Most of Alaska's lands and waters have few or no invasive organisms. But warming water and air make its freshwater and land habitats more open to invasion, putting its self-sustaining wild fish and wildlife at risk.

A recent analysis estimated that Elodea's continued spread would cost Alaska's commercial sockeye salmon fisheries a mean of $159 million a year — not counting subsistence and recreational losses. Protecting the state's fish and wildlife needs closer collaboration among agencies and with Alaska Native Tribes and other local groups.

The Bipartisan Infrastructure Law invests in the resilience and restoration of America's lands, skies and waters. Visitors will see repaired trails and campgrounds, invasive species removed, and healthy wetlands, grasslands and forests.

Sources

Based on "Preventing Elodea Colonization of Salmon Habitat," National Park Service; a work of the United States government in the public domain. Tobias Schwoerer's statement is rewritten in hubnx's own words.