Invasive Snails Detected In SoCal Rivers

The following is courtesy of the California Department of Fish and Wildlife: 

The California Department of Fish and Wildlife (CDFW) has confirmed the presence of New Zealand mudsnail (NZMS) within San Bernardino County. The invasive snails were found in both the Santa Ana River and designated wild trout stream of Bear Creek within the greater Santa Ana River Watershed.

Despite their small size, NZMS is a highly problematic aquatic species. At only 4 to 6 millimeters in length on average, dense populations of NZMS can displace and outcompete native species, sometimes by consuming up to half the food resources in a waterway that native insects and fishes would eat. The snails have been linked to reducing populations of aquatic insects, including mayflies, stoneflies, caddisflies, chironomids and other insect groups upon which trout and other organisms depend.

CDFW urges anglers, boaters, visitors and locals to “clean, drain and dry” all recreational items and fishing gear, which generally means anything that has gotten wet. It is important to leave any stream water, debris and organic plant matter at a recreational site in order to prevent the further spread of the snails. Once NZMS is established in a new habitat, it is impossible to eradicate it without damaging other components of the ecosystem. Boaters, anglers and others who may visit any body of water, within or outside of infested areas, are asked to decontaminate their equipment and follow the “clean, drain and dry” best practices for all equipment and clothing used in a waterway:

  • If you wade, freeze waders, wading boots and other gear overnight (at least six hours, though 24 hours is recommended).
  • After leaving the water, inspect waders, boots, float tubes, paddleboards, kayaks or any gear used in the water. Leave all water and debris at the site that you exited.
  • Additionally, remove any visible snails with a stiff brush, clean off soils and organic material, and follow this by rinsing at the site, preferably with high-pressure hot water.
  • It is critical to completely dry out gear for a minimum of 24 hours.
  • Never transport live fish or other aquatic plants or animals from one body of water to another.
  • An informational flier on the “clean, drain and dry” directive is available for download on CDFW’s website.

The Santa Ana River is the largest river completely in Southern California. Its flow begins in the San Bernardino mountains and concludes at the ocean in Huntington Beach. Bear Creek begins at Big Bear Lake and connects with the Santa Ana River in the mountains. The Santa Ana River watershed has a drainage basin size of 2,650 square miles, is home to 4.5 million people, and is popular among recreationalists and fishermen.

To date, NZMS has been identified in over 17 bodies of waters in the coastal Southern California counties of Ventura, Los Angeles, and Orange, including Lower Santa Ana River. NZMS-positive lakes and streams in the Eastern Sierra are in Inyo and Mono counties – Diaz Lake (Inyo), Pleasant Valley Reservoir (Inyo), Tinnemaha Reservoir (Inyo), Lone Pine Creek (Inyo), Lower Bishop Creek (Inyo), Bishop Creek (Inyo), Bishop Creek Canal (Inyo) and Los Angeles Aqueduct (Inyo); Owens River (Mono and Inyo); Upper Owens River (Mono), Hot Creek (Mono), Rush Creek below Grant Lake Dam (Mono) and Crowley Lake (Mono).

CDFW has launched public outreach and education efforts to discuss NZMS in San Bernardino County with local water districts, federal and state agencies, non-profit fisheries partners and fly fishing clubs. Greater outreach efforts will occur in the next few months and into the spring, including posting NZMS signage at Bear Creek angler survey boxes and at other water access points along the Santa Ana River.

For more information on NZMS , please visit the Invasive Species page on CDFW’s website. The U.S. Geological Survey’s website also features an interactive map showing the current distribution of NZMS  in California and throughout the U.S.

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