Georgia Wildlife Resources Division
2067 U.S. Hwy. 278, SE, Social Circle, GA 30025
New Zealand Mud Snails, Potamopyrgus antipodarum, were discovered in the U.S. in Idaho (Snake River) and Montana (Madison River) in the late 1980s. Since that time they have spread to most of the Western states with the exception of New Mexico.
Distribution map  (link to Montana State University site)
There is concern over this species due to its ability to reach densities of up to 120,000 per square yard in suitable habitats. In heavy infestations this snail can comprise over 95% of the invertebrate biomass in a river. Limited research in the Western U.S. has documented decreases in native macroinvertebrate populations in several rivers where the mud snail has invaded. It has also been shown to drastically alter primary production in some streams. Its invasion has generated much concern about the potential effects it may have on native species, fisheries, and aquatic ecosystems in the western U.S.
New Zealand Mud Snail photo from USGS/Florida Caribbean Science Center
Spread into new systems is considered to be primarily human caused. Anglers should be aware of this species and the potential for spread through contaminated equipment or clothing. There are ways to prevent the spread of ANS through angling and other recreational activities.
Tips for anglers and water recreation  (link to Stop Aquatic Hitchhikers site)
Controlling the spread of New Zealand mudsnails on wading gear  (link to California Department of Fish and Game pdf document)
NZ Mud Snail Alert Card  (pdf from ANS Task Force)