The Delaware River Watershed Initiative (DRWI; https://4states1source.org/) is a multidisciplinary collaboration of more than 70 organizations working to conserve and restore the streams that supply drinking water to 15 million people in New York, New Jersey, Pennsylvania and Delaware. The DRWI collaboration, enabled by leadership funding provided from the William Penn Foundation, facilitated environmental work across the basin to reduce water pollution, protect headwaters and promote water-smart practices and policies. Under this initiative, environmental, scientific, educational, and conservation organizations worked from 2014 to 2025 to protect and restore the Delaware River system in eight priority geographies, referred to as Clusters: Poconos-Kittatinny, Upper Lehigh, New Jersey Highlands, Middle Schuylkill, Schuylkill Highlands, Upstream Suburban Philadelphia, Brandywine-Christina, Kirkwood-Cohansey Aquifer. Strategies to protect and restore landscapes to promote good water quality included forest land protection, implementation of agricultural best management practices (e.g., riparian forest buffers, streambank fencing, barnyard manure management systems, soil conservation and health strategies like cover cropping), and green stormwater management infrastructure (e.g., rain gardens and infiltration basins). Overall, DRWI accomplishments directly related to DRWI work and William Penn Foundation funding include 26,414 acres of protected forests and more than 1,446 restoration best management practices covering more than 296,841 acres, including implementation of agricultural restoration and urban stormwater management projects.

The overall goals of the DRWI Pollution Assessment were to:
A. Identify hotspots of excess nonpoint source pollution (nitrogen, phosphorus, sediment) in stream reaches and catchments of the Delaware River Basin.
B. Quantify progress toward improving water quality by DRWI-style restoration and land protection activities, answering questions such as: What fraction of excess nonpoint source pollution has been reduced by DRWI and other projects? What level of investment is still required to achieve acceptable water quality? And
C. Report cumulative findings for each geography of interest, including DRWI-established Clusters and the Focus Areas within.