Interest in environmental DNA (eDNA) for the detection of aquatic invasive species (AIS) is increasing. Considering the invasion of zebra mussels Dreissena polymorpha into Lake Winnipeg in 2013, the development of eDNA monitoring methods may help managers prevent further spread of this AIS. For this thesis, sensitive and species-specific eDNA quantitative PCR assays and field/laboratory protocols were developed to be used for monitoring in western North America. These eDNA methods were found to be more sensitive for detection than was plankton netting for presence/absence of veligers. Environmental DNA target gene concentration and veliger abundance appear to be positively correlated. Furthermore, veliger abundance may account for much of the variation in eDNA detections. Refinement of eDNA methods is also presented here to improve detection. The work in this thesis provides considerations and guidelines for managers using eDNA as a detection tool for zebra mussels.