Wastewater testing in Casper and other Wyoming towns finds no evidence of invasive mussels By Brendan LaChance on July 7, 2021 Zebra mussel in a “marimo ball.” (Wyoming Game and Fish Department) CASPER, Wyo. — The Wyoming Game and Fish Department said on Tuesday that the department tested wastewater samples for a three-month period from March-June following the discovery of invasive zebra mussels in moss balls sold at some pet stores in Wyoming. The wastewater testing in Casper, Cheyenne, Laramie, Sheridan, Gillette and Rock Springs revealed no DNA evidence of zebra mussels. “These initial test results are promising,” said Game and Fish Director Brian Nesvik. “We’re glad to get negative results but we know zebra mussels are hearty and their life cycle is long. Continued monitoring remains important before we confidently know that zebra mussels have not spread in Wyoming.”