This article describes how a sustainable watershed-level planning approach is used to develop a flood-mitigation and stormwater management plan for an 11 km2 watershed in southeastern Pennsylvania, USA. West Ambler is an Environmental Justice (EJ) community located in the downstream portion of the watershed with socioeconomically vulnerable residents facing unequal distribution of environmental risks. This study uses a methodological framework based on the three dimensions of EJ (i.e., Distribution, Procedure/Participation, and Recognition) to address watershed concerns while managing risks within the EJ community. Although the project is scientifically grounded by a GIS-based watershed assessment and hydrologic and hydraulic modeling, all project components are influenced by one or more EJ dimensions, with an emphasis on community engagement and multi-municipal collaboration. Flood-mitigation suggestions are based on the evaluation of hundreds of stormwater management facilities throughout the watershed. This article explains the process of using an EJ framework in watershed-wide planning and management.