Freshwater mussels are one of the most imperiled faunal groups in North America, with over 70% of freshwater mussel species considered to be endangered, threatened, or of special concern. Causes for imperilment include habitat fragmentation, habitat degradation, and climate change. Traditional survey methods, such as snorkeling or using view buckets in transects or quadrats, are commonly used to measure freshwater mussel species presence and abundance; however, these methods are time-intensive and spatially limited, and it can be difficult to detect rare mussel species due to their patchy distribution and burrowing behavior. To overcome these difficulties, environmental DNA (eDNA) surveys, which use non-invasive water samples to assess species presence, have become a desirable tool for freshwater mussel conservation. In this study, we evaluated eDNA as a method for detecting brook floater (Alasmidonta varicosa), a state-listed endangered freshwater mussel species in Massachusetts, where only four viable populations remain. First, we sampled eDNA at sites with known populations of brook floater. At each site, water samples were collected upstream, immediately downstream, and 100 m downstream of the known population. In addition, habitat (e.g, wetted width) and water quality (e.g., pH, specific conductivity, dissolved oxygen, total suspended solids) were collected at each location. In the lab, water samples were filtered, DNA was extracted, and then amplified using qPCR. Once methods were verified at sites with known populations of brook floater, we sampled for brook floater eDNA at sites where the species has not been recently recorded to 1) identify the existence of brook floater and/or 2) determine potential for the reintroduction of stocked propagated mussels. Results will be used by managers throughout the brook floater range (Georgia to Nova Scotia) to inform expanded use of eDNA for species surveys and restoration efforts.