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Aquatic nuisance species, both plant and animal, pose a serious threat to the biological diversity of Washington waters. Many organisms have been spread unintentionally as hitchhikers on recreational vessels and gear. Once non-native species spread to a new environment with no natural predators, they often kill off native species and cause other biological, economic, and recreational damage. For example, 42% of the species listed under the Endangered Species Act became endangered by the introduction of non-native species.

Here are some aquatic nuisance species that have been found in Washington.

  • New Zealand mud snails: There are established populations of mud snails in the Columbia River at Young’s Bay and Kalama, in the Snake River on the eastern border of the state, and in waterways on the Long Beach Peninsula.
    • New Zealand mud snails are very small (about ⅛ of an inch long when full grown). Therefore, they are transported easily on gear and in live/bait wells. The snails can reproduce rapidly via asexual reproduction, so it takes only one to start a new infestation. They have no natural predators in the U.S.
    • Boaters visiting areas infested with mud snails need to clean their boats and gear with very hot water and let them dry out for several days. During the wet season, use a weak chlorine solution instead of water.
  • Aquatic weeds: Nearly every county in Washington is infested with some species of aquatic weed, such as purple loosestrife, giant hogweed, Eurasian water milfoil, hydrilla, spartina, or fanwort.
    • It only takes a small fragment to begin a new population of these invasive plants. Once introduced, they rapidly displace native plants and form single-species stands. These stands clog waterways and reduce aquatic habitat for fish, waterfowl, and aquatic mammals.
    • If boaters leave an area with weeds on their boats, those weeds also can carry a variety of other nuisance species.
  • Sea squirts: Several species of invasive sea squirts (also known as tunicates) have spread throughout the Puget Sound, turning up in Hood Canal, Birch Bay, Totten Inlet, Des Moines, and Neah Bay. Sea squirt infestation is becoming a critical issue in Washington.
    • Sea squirts have no known predators and can quickly cover the hull of boats, pilings, and other hard surfaces, suffocating other sea life. Sea squirts can attach to hulls and anchors and be spread if the vessel is moved from one body of water to another.
    • Three types of sea squirts have been discovered in Washington’s waters.
      • Clubbed tunicate (Styela clava), which is native to Asia. This type of sea squirt has very heavy infestations at Pleasant Harbor, Neah Bay, and Blaine.It tends to get on docks, boats, aquaculture lines, and cages.
      • Solitary sea squirt (Ciona savignyi), which is native to Asia. This sea squirt species is found at Eagle Harbor, Des Moines, and South Hood Canal.
      • Colonial sea squirt (Didemnum lahillei), which is native to Europe. This type of sea squirt is found in Okeover Inlet and around Vancouver Island. When transported, a small piece of the colony (less than a half-inch square) can form a new colony.
  • Zebra mussels: Although not yet a problem in Washington, zebra mussels are still very much a concern.
    • Zebra mussels are about an inch or less long. They attach to hard substrates and often are found in clusters. Because the mussels can live out of water for nearly a month, the possibility of them being transported to Washington via a recreational boat exists.
    • Zebra mussels have been found in states close to Washington, so boaters who travel out of state with their boats should clean their boats and gear thoroughly before putting them back into Washington waters.
  • Others: Other invasive animals that threaten Washington waters are Asian clams, Chinese mitten crabs, and European green crabs.
Quagga and zebra mussels
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