The California Department of Fish and Wildlife announced the discovery of an invasive species in Lake Tahoe.

According to a CDFW release, divers monitoring the lake for aquatic invasive species detected New Zealand Mud Snails (Potamopyrgus antipodarum) off Lake Tahoe’s South Shore. 

The mud snails are tiny, aquatic snails that reach an average length of four to six millimeters, the Department of Fish and Wildlife said.  

New Zealand Mud Snails were first discovered in America in 1987 in the Snake River in Idaho, and were found in California in the Owens River in 2000. They were believed to have been introduced to western rives through shipments of live sportfish, but subsequent spread is likely due to recreational activities, CDFW officials said.

They have a prolific reproductive system; mature female mud snails can produce 230 new females asexually every year, and scientists estimate that one snail and its offspring can result in over 2.7 billion snails within four years.

“Despite their small size, [the snails] are a highly problematic aquatic species,” CDFW officials said. “Dense populations can displace and outcompete native species, sometimes by consuming up to half the flood resources in the waterway.” 

Invasive New Zealand Mud Snails discovered in Lake Tahoe
New Zealand Mud Snails (Potamopyrgus antipodarum) off Lake Tahoe’s South Shore. (California Dept. of Fish and Wildlife)

The snails have been linked to reduced populations of aquatic insects that trout and salmon populations in the lake depend on. 

“This is a significant detection and one we are treating with the utmost seriousness and urgency to determine the extent of the infestation and prevent any further spread within the Lake Tahoe watershed,” said Colin Purdy, Environmental Program Manager for CDFW’s North Central region, which includes the California portion of Lake Tahoe and most of Placer and El Dorado counties. “It will take a coordinated commitment by all the entities that serve the Tahoe Basin as well as the public to prevent further spread of these invasives in a lake and watershed that’s cherished around the world.” 

Unfortunately, once the New Zealand Mud Snails are established in a new habitat, they are impossible to eradicate without damaging other components of the ecosystem, CDFW said. 

Officials are urging anglers, boaters and visitors to “clean, drain and dry” all recreational items, fishing gear or any other piece of equipment that has gotten wet, as well as any clothing items that got wet. Any stream or lake water, debris and organic plant matter should be left at a recreational site to prevent further spread of the snails. 

Other practices that individuals can take to mitigate the spread of the New Zealand Mud Snails include: 

  • Freezing waders, wading boots and other gear overnight (at least six through 24 hours is recommended) 
  • Inspecting waders, boats, float tubes, paddleboards, kayaks or any gear used in the lake after leaving the water and leave all water and debris at the site 
  • Removing any visible snails with a stiff brush, cleaning off soils and organic material and rinsing with high-pressure hot water at the site 
  • Never transport live fish or other aquatic plants or animals from one body of water to another 

Scientists with the Department of Fish and Wildlife are in the process of developing and implementing plans for sampling bodies of water around the Tahoe Basin to better define the invasive species’ geographic range. 

Sampling areas will include high-traffic areas, boat launches, access points, coves, inlets and outlets, and side channels. As of Thursday, the snails were not identified in any of the surrounding waterbodies, however the snails have been detected in several lake and river systems throughout California and nearly all of the western United States.

To report an invasive species sighting to the California Department of Fish and Wildlife, click here

Click here to view CDFW’s Aquatic Invasive Species Decontamination Protocol.