Nutria, or coypu (Myocastor coypus), are invasive semi-aquatic rodents present across the United States, Europe, and Asia. Despite successful eradication efforts in certain areas, nutria have resurged in the mid-Atlantic USA, underscoring the need for advanced monitoring tools. Environmental DNA (eDNA) has emerged as a promising technique for species detection and monitoring. Here, an eDNA assay for nutria was field-validated in Virginia, USA, showcasing its potential as a tool for post-eradication monitoring. The findings reveal an association between water levels and nutria eDNA detection, highlighting the importance of water levels in nutria behavior. A painted turtle assay was introduced to confirm nutria absence and demonstrate the potential of passive sampling. The study showcases the sensitivity and efficiency of eDNA assays, emphasizing their value for monitoring and verifying eradication.