In the 500 or so years since Europeans sailed to North America, ships, trains, automobiles, and planes have given humans the ability to easily transport themselves anywhere on the continent, and all over the world. Plants and animals familiar and comfortable to these travelers were and are also taken along for the ride, and even more organisms are unintentional travel partners. Some of these organisms are unable to adapt to changes in climate, but plenty of others have found a new home where they can flourish free from the competition, predators, and disease that controlled their populations abroad.

Ships' ballast, boat motors, bait fishermen, and aquaculturists have introduced hundreds if not thousands of species to North American waters. The microscopic animals that float around in estuaries have been nearly replaced by foreign species in some sea ports; very young zebra mussels survive quite well in the water retained in outboard motors; and fishermen sometimes don't know of the potential consequences when they dump the crayfish or worms that they were using for bait. But these aren't the only avenues for human dispersal of aquatic organisms.

State and federal fish and wildlife agencies have moved fish all over the country and introduced quite a few fish from other countries, and though many lessons have been learned, the introduction of nonindigenous fish continues to this date. Fish weren't their only target though. In the 1930's, the predecessor to the Oregon Department of Fish and Wildlife also introduced amphipod crustaceans from Utah and Nevada into the Willamette Valley, presumably to enhance food sources for fish. Other Pacific Northwest waters have not been without their share of introductions, and it seems more species are on their way.

A short list of introduced species is included below. Some taxa have links to the section of the guide with the most pertinent information. Others have links outside this guide and will only work if you're on-line. Additional links are provided below the partial introduced species list, or you can do web searches for any of the names below or for "nonindigenous species freshwater."

Invasive species lists and general information

USGS nonindigenous freshwater species (outside link)
USGS site for introduced crustaceans in North America with pictures and maps of selected introduced species (outside link)

Species pages

• Chinese mitten crab - non-native invasive in CA, native to China (outside link)
  
• Orconectes virilis - virile crayfish - nonnative invasive, widespread (outside link)
  
• Orconectes immunis - calico crayfish - nonnative invasive in parts of MT (outside link)
• Orconectes neglectus - ringed crayfish - nonnative invasive in southwest OR (outside link)
• Procambarus clarkii - red swamp crayfish - nonnative invasive, widespread (outside link)
  
• Procambarus acutus - white river crayfish - nonnative invasive in CA (outside link)