Many native fish populations across the West face increasing threats from non-native and invasive species.

Often inadvertently introduced, some invasives have a direct effect on fish populations. Whirling disease is spread by a tiny parasitic organism (Myxobolus cerebralis) that attacks the nervous system and cartilage, causing higher mortality rates in native fish populations. New Zealand mud snails (Potamopyrgus antipodarum) have an indirect effect on fish by outcompeting native aquatic insects and, in turn, providing less food for fish.

Quagga mussels (Dreissena bugensis), a close relative to Zebra mussels, were found in Lake Mead National Recreation Area in January 2007. These mussels are over 1,000 miles from the nearest other population, so they most likely hitchhiked via boats. They eat large amounts of phytoplankton, affecting the aquatic food chain. They may also clog water intakes on boat engines and even municipal water systems.

Invasive plant species can also prove detrimental to native fish populations. Tall whitetop (Lepidium latifolium) crowds out native bankside vegetation that is vital for providing shade and cover for native fish and preventing erosion. Cheat grass (Bromus tectorum) outcompetes native plants, creating monocultures along streams and adjacent uplands that make them more susceptible to wildland fires.

You can help control the spread of non-native and invasive species. Please do not transport live fish or fish parts from one drainage to another. Also, when you change fishing locations, rinse all mud and debris from fishing equipment and wading gear and drain water from boats before leaving the area. Thoroughly wash boats, trailers, and vehicles before heading out on your next trip. If you have been fishing in an area that is known to have whirling disease (such as in Utah or Montana), disinfect your gear by spraying a 10% bleach solution on it, then rinsing it after 15 minutes and letting it dry in the sun.