Freshwater Mussels (Unionidae) play a critical role in aquatic ecosystems and are one of the most rapidly declining groups of organisms across the globe due to habitat loss, water quality degradation and urbanization. The discovery and protection of existing populations is critical to the understanding of their decline and unexpected success, especially in the Delaware River watershed (USA). Surveys spanning 2024 and 2025, 1,123 Unionidae mussels were documented in the Darby Creek Watershed (southeastern Pennsylvania, USA) as a result of the Darby & Cobbs Creek Community Science Program (DCCCS) long term volunteer monitoring effort. Through monthly water chemistry data collection, Elliptio complanata shells had been documented by a DCCCS volunteer in the watershed as early as December 2022, and beds of live freshwater mussels were found the following spring 2023. In 2024, a qualitative survey was conducted leading to the discovery of 853 total Unionidae, including 849 mature E. complanata, two juvenile E. complanata, and two mature Utterbackiana implicata. In 2025, an additional 260 E. complanata and one U. implicata were documented. However, population density declined significantly below a small unnamed tributary (p = 0.0006). The unnamed tributary to Darby Creek had no mussels present and significantly higher conductivity throughout the year when compared to Darby Creek above the confluence (p = 0.033) suggesting unknown contamination prohibiting further recruitment in that waterway despite the presence of suitable habitat. The documentation of this novel mussel bed represents a significant historic population, challenging long-standing assumptions about habitat suitability in this urban watershed and highlighting the need for further investigation in nearby waterways. The presence of juvenile mussels suggests active recruitment, highlighting potential resilience despite environmental stressors. Results underscore the value of DCCCS volunteer efforts in biodiversity monitoring and conservation and suggest the need for targeted habitat protection and restoration efforts. This study provides a foundation for future research on mussel-host fish dynamics, water quality improvements, and long-term population trends in urban freshwater ecosystems.