Since 1992, the NOAA Great Lakes Mussel Watch Program (GLMWP) has collected invasive zebra and quagga mussels from sites in the Great Lakes as part of its national contaminant monitoring program. Zebra and quagga mussels store contaminants in their bodies, a quality that suggests they may be useful as water quality biomonitors. Because they are stationary filter feeders, are abundant, and are relatively resistant to chemicals, their body tissues can be tested to reveal pollution where they live. In 2018, a team of marine scientists from the NOAA Marine Debris Program, NOAA GLMWP, and Loyola University Chicago joined forces to ask whether these invasive mussels take in microplastics along with chemical pollutants, and might they be indicators of microplastic pollution in the Great Lakes?