Modeling watershed biogeochemistry has long relied on the assumption that wastewater infrastructure provides predictable, discrete point sources of nutrients and energy. Under well-maintained conditions, these point sources can be accurately quantified and integrated into models for reliable assessments of nutrient dynamics in urbanizing watersheds. However, interactions among aging infrastructure, shifting climate conditions, and continued urban development challenge this paradigm through unintentional infrastructure failures. Here, we consider how aging systems, originally designed as controlled point sources, now operate more like intermittent nonpoint sources. Specifically, we examine two decades (2000–2019) of publicly available sewage spill records in two counties within the City of Atlanta, documenting 6,732 reported spills with a total estimated volume of 3,491,750,429 liters of untreated wastewater discharged into the Chattahoochee and South River Basins. The average spill volume of 518,603 liters highlights the potential scale of unintended nutrient loading, amounting to thousands of kilograms of carbon, nitrogen, and phosphorus introduced into local watersheds. Such episodic, high-volume spills can complicate the development of realistic watershed biogeochemical models, which often do not account for failing infrastructure. Using Atlanta as a case study, we illustrate why framing unintentional spills as emergent nonpoint sources may be critical to improving predictive accuracy in the face of deteriorating wastewater systems, an increasingly common challenge in the United States and many other regions around the globe.