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New Zealand Mudsnails Pose Massive Risk to Our Waters

Our local waters are at detrimental risk of the invasive New Zealand Mudsnail that has been found in Bellevue's Kelsey and Valley Creek.

If you enjoy visiting our local lakes and streams, you’ll want to read this.  You know that old science-fiction, horror movie, The Blob?  When I found out what’s going on in nearby streams, the movie immediately came to mind.  The Blob is a giant amoeba-like alien that eats everything in its path and grows exponentially.  While we have not encountered the Blob’s distant cousin, we have encountered a creature that eats everything in its path and reproduces at unbelievable rates.  What we have encountered is the invasive aquatic New Zealand mudsnail (NZMS), which has brought its super villain powers to some of our favorite Eastside creeks all the way from…New Zealand. 

The NZMS is a freshwater aquatic snail that can be as small as a grain of sand (4-6mm), and it has proven to be detrimental to aquatic systems throughout the country (click here for distribution map).  The easy-to-spread mudsnail has been found in Bellevue’s Kelsey and Valley Creek, and the terrorizing has already begun and won’t stop.  Here’s why. 

The NZMS has mastered three hobbies: cloning, eating, and staying alive.  Parthenogenetic, the mudsnail is asexual and quickly reproduces clones all by itself.  Just one NZMS can result in a colony of over 40 million snails in one year.   Mother and her family of millions chow down on plant and animal detritus (waste) and algae, outcompeting native aquatic snails and insects that other species depend on for food.  Algae are the primary producers for the entire food web of an aquatic system.  What happens when you pull out the bottom block of a Jenga tower, or the primary producers out of a food chain?  The blocks on top, or the higher-trophic level species, are not sustained.   As the NZMS population increases, a habitat’s food web is disrupted, fish growth and populations are reduced, and vegetation and other native life are impacted. 

Ready for the perfect storm?  The NZMS has an operculum, or a lid, that can seal the opening of its shell, protecting it from just about anything, including exposure to chemicals.  Safe inside, a NZMS can even survive the digestive system of animals.  The snail comes out the other end of a fish or bird, happy and whole into a new habitat to begin colonizing.  The NZMS can survive cold temperatures and being out of water for weeks if in damp, cool conditions.  “Stay together” is a survival skill that we humans learn at a young age, and the NZMS are experts.  The mudsnails pack tightly on rocks, gravel, mud, sand, and vegetation with densities as thick as 400,000 in one square meter.  These aquatic snails can survive bleach, being out of water for extensive time, and the horror of a digestive system.  This means that once the NZMS is established in a habitat, it is impossible to eradicate them without damaging other parts of the ecosystem.  Like I said, it’s the perfect storm. 

While we can’t kill off the mudsnails, we can prevent them from spreading.  The NZMS is considered an aquatic hitchhiker, which is how they arrived here from New Zealand.  Examples of the mudsnail’s travel methods are attaching to boats, fishermen and scientist gear, recreationists’ clothing, and dog fur.  If the NZMS spreads, you can say goodbye to walking barefoot in a lake or stream on a sunny afternoon.  You can say goodbye to having any luck while fishing, or seeing your child’s excitement when they yell, “I saw a fish!”.  You can say hello to snail infested waters in which enjoying becomes just a memory.  Don’t forget, not all snails are bad.  Please don’t despise all snails, but do understand that identifying the difference between native aquatic snails and the NZMS is very difficult.  With that said, here’s how to prevent spreading the NZMS:

  • Stay out of water that is known to be inhabited by the NZMS.  So far in Washington, that means the lower Columbia River, Olympia’s Capitol Lake, the Long Beach peninsula, Thornton Creek, Lake Washington, and now Kelsey and Valley Creek
  • Use separate gear for aquatic systems that have been invaded and for those that haven’t.  Avoid cross-contamination.      
  • Thoroughly brush off any debris from waders, boots, and equipment that came in contact with stream or lake water.  Wash the gear in hot water at 140°F (not recommended for GORE-TEX®) or freeze at or below 26°F overnight.
  • If not using hot water or freezing overnight, soak gear for 10 minutes in commercial disinfectant solution containing quaternary ammonium compounds (QAC), such as Formula 409®.  Do not dispose of the used solution or rinsing water into a drain that does not lead to a water treatment facility.  QAC is a known chemical to kill the NZMS. Take that, warrior shell!   
  • Dry all gear for 48 hours before reuse.
  • Clean, drain, and dry any watercraft after use.


If you are able to see dirt on your gear, assume that it is not decontaminated properly.  Remember, it only takes one snail to disrupt an entire ecosystem.  Let’s all do our part by practicing thorough prevention and decontamination.  Also, please spread the word in every way that you can.  Come on Eastside, let’s put up a fight.  Stay out and stay dry! 

Suggested Resources:

-Mud snails withstand salt water bath, The Olympian

-How to Prevent the Spread of New Zealand Mudsnails Through Field Gear

-Washington Invasive Species Council

-Mudsnails.com

-New Zealand Mud Snail, Potamopyrgus antipodarium (Gray)

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

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