A one-dimensional surface-water quality model of the central Salem River Basin, New Jersey was developed to examine the causes of eutrophication and predict the effects of reduced point and nonpoint source nutrient loads on water quality. The model was developed using the USEPA WASP code. The model simulates channel flow and the fate and transport of dissolved oxygen, oxygen demands, nutrients, and phytoplankton chlorophyll-a in the main stem river and largest tributary from April 1, 2007 to October 31, 2008. Continuous and discrete water-quality data from the Salem River were collected during this period to help build and calibrate the model. The calibrated model was used to evaluate the effects of (1) natural conditions and (2) an extreme reduction in nutrient loads. The scenarios involved reduction of nonpoint and point source nitrogen and phosphorous inputs to the river from the adjacent watershed and riverbed. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20225047)