SOUTH LAKE TAHOE, Calif. – Divers are currently assessing the status of New Zealand mudsnail populations once again after almost one year from their initial discovery in Lake Tahoe. As the first invasive species discovered since before 2008, the finding last September was quite alarming when divers on a routine invasive weed survey came across the small invaders offshore near South Lake Tahoe.

With Lake Tahoe’s world class motorized watercraft inspection program launched in 2008—inspecting over 100,000 boats, performing 55,000 decontaminations and intercepting all motorized watercraft before they hit the lake—the Tahoe Regional Planning Agency and partners have been scratching their heads on how exactly the new invader got here.

Although they may never know for sure, one clue to the mystery is where divers found the snails. “…not in a place you would normally find them,” TRPA Aquatic Invasive Species Program Manager, Dennis Zabaglo, says, “They’re called mudsnails for a reason.”

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He notes the rice sized snails typically take up residence in river banks, creeks, and streams. But contrary to that, they were initially found far from shore, about 2,000 feet out.

Zabaglo says this is indicative of a nonmotorized vessel, “…a floaty, kayak, or canoe, or paddleboard.” Even beach toys or angler equipment could have been the culprit.

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The area of discovery is a popular walk in recreation spot along south shore, another indicator for non-motorized transfer along with the fact that surveyors have not found the snails at nearby boat ramps or motorized watercraft launch facilities. In addition, the snails distance from shore coincides with the low water levels during the year they believe they were likely introduced, which the TRPA suspects was a year or two before they were discovered in 2023.

Upon discovery, the TRPA and partners sent divers into the lake to delineate the infestation. Luckily they did not find the snails outside the initial area of discovery and found them concentrated to the area of south shore in line with Ski Run Boulevard running west and ending around Pope Beach.

Once region partners knew the extent of what they were dealing with, they faced another question. What do they do about it?

“Unfortunately, with New Zealand mudsnails, there’s not a recognized control method to treat them,” Zabaglo explains. Fisheries and hatcheries have had some success with pesticides, but Zabaglo says those aren’t options for open water situations.

“So, our best efforts right now,” Zabaglo continues, “are containment and trying not to spread them elsewhere throughout the lake.”

While Tahoe has its motorized inspection program, when spreaders can be as unassuming as beach toys or fishing waders, it can make containment feel all the more daunting. Modern conveniences have also made this a challenge.

“Part of the reason it is so hard to control the non-motorized users is, as you all have seen, you can just put on a backpack with your paddleboard now and go down to any single spot on the lake,” Community Engagement Manager Victoria Ortiz says, “it’s really hard to regulate.

That’s why as a response to the new infestation, region partners, including the TRPA and League to Save Lake Tahoe, have increased public outreach to non-motorized users, educating them on how they can help prevent spread.

“Clean, drain, dry, is our mantra,” Zabaglo says. It’s likely something anyone who has been in Tahoe for some time has now heard or come across.

Since many invasive species can stowaway and survive in even just one drop of water for some time, it’s important to clean anything that touches water. The next step is to drain the object, so no residual water can remain. Finally, dry it, and keep it dry for seven days before heading to a new water body or different part of Lake Tahoe. If you can’t wait the seven days, the Tahoe watercraft inspection stations can decontaminate your nonmotorized vessel free of charge.

“What people don’t realize is that even if there’s any water on on say your PFD, life jacket, or inside your paddle,” as Ortiz says many have removable paddles, “if there’s water stuck in there, you could have any invasive species continuing to live in there.”

According to the UC Riverside Center for Invasive Species research, New Zealand mudsnails can survive out of water for up to 24 hours and up to 50 days in just a damp environment. In addition to reproducing sexually, they can also reproduce asexually and one snail can produce around 230 offspring a year, so all it takes is one. Their small size often makes them easy to miss.

In addition to public outreach and education, region partners are making cleaning, draining and drying convenient for recreators with the help of a certain device.

“The CD3 machine is about the size of an NBA player, maybe seven feet or so by maybe four feet…” Ortiz describes the device. The CD3, which stands for clean, drain, dry, dispose is a machine stationed at certain popular non-motorized recreation spots with a vacuum, air hose, and other tools to help people abide by the clean-drain-dry mantra.

To really get savvy on clean-drain-dry, anyone can become a Tahoe Keeper and join a community of informed non-motorized recreators who have completed a short video and quiz, supplying the know how of gear related aquatic invasive species prevention. The TRPA has recruited paddleboard and kayak beach concessionaires into the Tahoe Keeper community so they can inform those who use their equipment.

Clean-drain-dry isn’t something to just abide by before hitting Tahoe’s water. “Now we know, Tahoe has some invasive species that other regional water bodies do not,” Ortiz says, “so not only is it important to make sure you clean, drain, dry before you enter Lake Tahoe, it’s also critical to do it when you leave Lake Tahoe.”

Although an extra step, Zabaglo explains why keeping aquatic invasive species out of water bodies is important, not just from an ecological standpoint but from a recreator’s experience as well.

“Most of these aquatic invaders that are present here in Tahoe are in those areas in the near shore where our locals and visitors experience the lake.” He says the weeds can especially ruin that experience and create concentrated areas where algae can thrive and impact Tahoe’s famed clarity.

They can also outcompete native species and create a habitat suitable for more invasive species.

Agencies are anxiously awaiting results from the dives currently taking place. The results will reveal how the population of New Zealand mudsnails has expanded or moved and how their densities have changed.

Something Zabaglo says experts see nationally with these populations is a boom and bust pattern in which the dense population found at first discovery gradually thins after some time.

The TRPA is also monitoring potential spread through environmental DNA analysis, sampling 300 tributaries around the lake, including north shore.

It’s unclear whether the new snails will become a permanent underwater fixture of Tahoe, but Zabaglo says continued monitoring will provide that answer.