Urban watersheds draining to Poverty Bay (King County, Washington, USA) have experienced persistent fecal pollution, resulting in closure of 825 of the area’s 1,100 acres of commercial shellfish growing areas. Multiple sources, including aging side sewers, onsite sewage systems (OSS), and diffuse nonpoint inputs typical of urban basins, make these watersheds difficult to diagnose and restore. The King County Pollution Identification and Correction (PIC) program addresses this challenge through a collaborative, science-based approach that pairs targeted monitoring with coordinated corrective action across agencies and disciplines. From 2023–2025, the PIC team conducted a source-tracking study in Massey Creek, one of five urban subbasins discharging to the shellfish beds. We implemented a phased workflow designed to isolate likely sources, narrow down hotspots within the stream and stormwater conveyance network, and coordinate in parallel with outreach specialists to address both point and nonpoint contributions. The field science team conducted wet- and dry-season sampling of fecal indicator bacteria across the creek and stormwater system, then pursued hotspots using targeted DNA biomarkers and conductivity loggers to identify potential sewage signals. Field observations and sanitary surveys informed outreach priorities for pet waste management and OSS/side sewer maintenance. Across the study, we collected over 800 samples for fecal indicator bacteria analysis. This iterative approach led to investigation and correction of a failing septic system discharging to the Massey Creek mainstem. Following cleanup and connection to sewer, fecal bacteria concentrations declined by over 30%. Water quality improvements were bolstered by the collaborative nature of this project, including pairing financial assistance and public outreach work with field sampling efforts. The Massey Creek study provides a transferable framework for managing fecal pollution in complex urban watersheds and highlights the necessity and benefits of collaborative freshwater management and science.