This project developed an early detection molecular assay for detecting and quantifying zebra and quagga mussel DNA in environmental mixtures of the two species. At present, the assay is applicable to plankton tows containing veliger larvae, but it could be easily modified for midwater or lake-bottom samples as a more conventional “eDNA” assay. It is a highly sensitive test. The greatest contribution of this test is the simultaneous detection of both species, present together in the same water samples, since there is at present no convenient, reliable method for separately quantifying larvae from quagga and zebra mussels in mixtures. Recently we showed that there is no apparent bias in estimating the relative abundance of DNA from both species, and we showed that the assay reliably quantifies veligers, even in tow samples that are filled with DNA from other species of planktonic animals. Because several water bodies have both species; quagga reproduction in Minnesota is unknown; adults in the upper Mississippi River in Minnesota are scattered but in fairly high numbers (in important potential source locations like Lake Pepin); and more broadly since quaggas have replaced zebra mussels in the lower Great Lakes, further application of the assay to estimate reproductive output of the invader—still on the horizon for Minnesota—would be useful.