By Matthew Hersh
Beneath Princeton’s streets lie invisible boundaries that determine where every raindrop goes, dictating how rainfall, runoff, and streams travel.
These boundaries, known as watersheds, are land areas that channel water into a single river system and play an important role in how communities share water resources and address environmental challenges. This year, Princeton is moving forward with a major initiative to better understand and improve local water quality across the municipality’s watersheds as the town identifies contaminants and assesses environmental conditions throughout its waterways.
“So far, the project has centered on characterizing contaminants and compiling a Phase One inventory report,” said Deanna Stockton, municipal engineer and deputy administrator. Upcoming meetings with consultants will shift the focus to the second phase, or a Watershed Assessment Report, which would identify potential runoff remediation projects, which could include green infrastructure measures such as pavement, rain gardens, expanded tree planting, and filtration systems designed to address issues like low dissolved oxygen levels or bacterial contamination, Stockton said.
The effort covers all eight of Princeton’s watersheds, including the most prominent, the Stony Brook and Lower Millstone systems, as well as smaller sub-watersheds, characterized by the New Jersey Department of Environmental Protection (NJ DEP) as HUC-14 level waterways, and include segments of Stony Brook, Harry’s Brook, the Millstone River segment near Harrison Street, Heathcote Brook, and Lake Carnegie. Officials say this detailed approach allows the Municipality to pinpoint pollution sources and develop targeted solutions rather than relying on broad regional strategies.
The initiative is part of a broader statewide watershed planning requirement affecting municipalities across New Jersey. While technical assistance is available through programs such as Rutgers University support services, much of the work remains largely unfunded, posing challenges for many communities, said Stockton, who emphasized the necessity of these partnerships.
Stockton said the project represents a long-term environmental investment aimed at protecting water quality, guiding future planning decisions, and educating the public about watershed health. As planning progresses, Princeton expects each watershed to follow a similar process — assessment, community discussion, and implementation of improvement projects.
The western side of town drains into Stony Brook, while rainfall in eastern Princeton flows toward the Millstone River. These waterways eventually merge into the larger Raritan River system, linking local environmental conditions to downstream communities, according to the NJ DEP.
This natural divide influenced Princeton’s development long before modern environmental planning existed, according to Sustainable Princeton. When Nassau Hall was constructed in 1756, builders selected a high ridge that today is recognized as the crest separating the two sub-watersheds. Water falling on one side flows west toward Stony Brook, while water on the other side travels east toward the Millstone River. Princeton High School was later built along the same elevated ridge.
Today, scientists and residents can trace these drainage patterns using tools such as the U.S. Geological Survey Streamer Map and Rowan University’s interactive Watershed Explorer, which visualize floodplains, impervious surfaces, and watershed boundaries, Stockton said.
Understanding watershed systems is essential for managing stormwater, protecting drinking water supplies, and reducing flooding risks, said Stockton, “Because water connects communities across an entire watershed, local land use decisions in Princeton can have lasting impacts far downstream.