Mud Snails in South Boulder Creek

Update (August 2021): Upon discovery of invasive New Zealand mudsnails in South Boulder Creek downstream of South Boulder Road in 2020, City of Boulder Open Space and Mountain Parks (OSMP) initiated a management review to make recommendations to stop further spread of this harmful species. After thorough review, an interdisciplinary team recommended the following management actions:

1. To decrease the likelihood that they will serve as a source of spread, OSMP will close select already-infested stream reaches with particularly high densities of NZMS:
• Dry Creek downstream (north) of Baseline Road
• Four Mile Canyon Creek on either side of CO-119
2. To prevent the spread of NZMS into particularly high-quality, uninfested habitats, OSMP will also close access to:
• Four Mile Canyon Creek upstream (west) of Broadway
• South Boulder Creek upstream (south) of South Boulder Road

OSMP recognizes the impact that loss of creek access will have on its visitors, especially anglers. These measures are intended to prevent irreversible degradation to some of the most important aquatic resources on the Front Range.
For more information, please review the Open Space Board of Trustees (OSBT) meeting agenda/memo available on the OSMP website or call Adam Gaylord (OSMP Ecologist) at 303-495-8982.

Help City of Boulder Open Space and Mountain Parks Stop the Spread of New Zealand Mudsnails
New Zealand Mudsnails are an invasive aquatic species negatively impacts local fish populations and disrupts ecological food webs by displacing native macroinvertebrates.
What Are They?
• Invasive aquatic snails from New Zealand
• Accidently introduced to US in 1987, now in streams and ponds across the western US and Great Lakes region, including Colorado
• First discovery in Colorado was in Boulder Creek in 2004, now found in 10 counties throughout the state
• Since 2004, the snails have spread around Boulder and are now found in Boulder Creek, Dry Creek, 4-mile Creek, South Boulder Creek, Wonderland Creek, Goose Creek, and Elmer’s 2-mile Creek

What’s the Problem?
• They’re tiny!
o Adults are about the size of a grain of rice and immature snails are even smaller
• They’re clingy!
o Because they’re so small, they can sneak aboard almost anything including waders, boots, and tackle. If it can carry a sand grain, it can carry a mudsnail.
• They’re hardy!
o NZMS can survive out of water for days
• It only takes one!
o NZMS reproduce asexually so a single mudsnail can result in a colony of 40 million snails in just one year.
• They’re tenacious!
o Once they establish in a creek, it’s practically impossible to get rid of them.
• They’re bad news!
o NZMS can achieve densities of over 70,000 snails per square foot. They displace native aquatic invertebrates (which fish eat) and pass through fish digestive systems without being digested. Ultimately this can result in reduced growth rates and lower populations of fish.
What can anglers do?
• Stay out of closed areas.
• Even if an area is open, if possible, avoid entering infested waterbodies.
• If you do enter an infested area:
o Before you leave the field:
– Clean your gear of mud/vegetation with a wire brush
o Back at home, do one of the following:
– Freeze your gear overnight
– Soak gear in hot water (at least 140°) for at least 10 minutes
– Submerge gear in 1:1 solution of water and Formula 409® for at least 10 minutes (Note: simply spraying gear with disinfectant does not work)
– Thoroughly dry your gear for at least 48 hours, preferably in direct sunlight

For more information, please see Colorado Parks and Wildlife’s New Zealand Mudsnail page: