November 3, 2026.
First detection in the southern Lower Peninsula prompts expanded monitoring and warnings to anglers and recreational water users.
The Michigan Department of Natural Resources (DNR) has confirmed the presence of invasive New Zealand mudsnails in Bear Creek, a coldwater tributary of the Thornapple River in Kent County. The discovery marks the first confirmed detection of the invasive species in Michigan's southern Lower Peninsula and raises concerns about its potential impact on native aquatic life and freshwater ecosystems.
The discovery also highlights an important geographic distinction: although New Zealand mudsnails have previously been documented in six northern Michigan river systems, all six are located in the Lower Peninsula. The DNR's current list does not identify any established populations in Upper Peninsula rivers.
The tiny snails were collected by volunteers with the Coldwater River Watershed Council during routine monitoring of aquatic macroinvertebrates, small organisms that live near the bottom of waterways and provide important indicators of water quality and stream health.
Volunteers initially submitted photographs to the Michigan Department of Environment, Great Lakes, and Energy for identification. Samples were subsequently examined by experts from Oakland University and Trout Unlimited, who verified the discovery.
New Zealand mudsnails were first identified in Michigan in 2015. Before the latest discovery, populations had been documented in the Au Sable, Boardman, Grass, Pere Marquette, Pine and Upper Manistee rivers. All six are in the Lower Peninsula.
The Bear Creek detection is approximately 75 miles south of the nearest previously known infestation in the Pere Marquette River.
A small invasive species with significant consequences.
New Zealand mudsnails are brown to black and measure approximately one-eighth of an inch in length. Despite their small size, they can reproduce rapidly and establish large populations.
The species reproduces without fertilization, meaning a single female can establish a new population. One snail can produce more than 200 young in a year.
With few natural predators or parasites in North America, populations can expand rapidly. Researchers have documented densities reaching 300,000 snails per square meter in some Western waterways. This figure reflects documented infestations outside Michigan, not population measurements from Bear Creek.
Large populations compete with native aquatic organisms for food and habitat. This can reduce the availability of important food sources, including mayflies and caddisflies, which are essential components of freshwater food webs.
The effects can extend to fish populations. Although fish may consume the snails, their hard shells make them difficult to digest and provide little nutritional value. Some snails can pass through a fish's digestive system alive.
As invasive mudsnails replace native food sources, fish may experience reduced growth and condition. These are documented concerns associated with the species, although no such impacts have yet been established in Bear Creek.
Monitoring expands in southern Michigan.
Michigan Invasive Species Program biologists are gathering additional information about the Bear Creek discovery and plan to conduct further sampling at the site and other Thornapple River tributaries in Barry, Kent and Ionia counties.
Genetic testing is also planned through Oakland University to help determine the source population. Officials have not yet established how the snails arrived in Bear Creek.
Informational signs will be installed at recreational access points along affected creeks and rivers.
The DNR says there are currently no effective treatments available to manage or eradicate established New Zealand mudsnail populations. Preventing the species from spreading to additional waterways is therefore a priority.
State officials will work with local conservation organizations, including the Coldwater River Watershed Council, Thornapple River Watershed Council and cooperative invasive species management areas, to increase public awareness.
Anglers and boaters urged to help prevent the spread.
Because the snails are extremely small, they can be transported between waterways on fishing equipment, waders, boots, nets, boats, trailers and other recreational gear.
The DNR encourages anglers, boaters and other people who spend time on Michigan's waterways to inspect and clean equipment before moving to another location.
Removing mud, plants and debris is an important first step. Boots and waders should be cleaned and disinfected according to DNR recommendations, including brushing, rinsing after the recommended treatment period and allowing equipment to dry thoroughly.
The New Zealand mudsnail's ability to reproduce from a single individual makes preventing accidental transportation especially important.
Michigan residents are encouraged to report suspected discoveries and learn more about identifying and preventing the spread of aquatic invasive species.
Additional information and reporting resources are available at Michigan.gov/Invasives.
The Michigan Invasive Species Program is jointly implemented by the Michigan Department of Environment, Great Lakes, and Energy; the Michigan Department of Natural Resources; and the Michigan Department of Agriculture and Rural Development.
