A previously developed groundwater-flow model of the Great Egg Harbor and Mullica River Basins, N.J. (https://doi.org/10.3133/sir20125187) by the U.S. Geological Survey (USGS) was used to analyze the effects on groundwater levels and stream base flow from possible changes in groundwater withdrawals and effluent infiltration in Winslow Township, Camden County, New Jersey. The Camden County Municipal Utilities Authority (CCMUA) infiltrated treated sewage effluent at their infiltration/percolation lagoons in Winslow Township, New Jersey, from 1985 to 2014. Increasing effluent volumes strained the capacity of the sewage-treatment plant and infiltration/percolation facility which closed in 2014. The treatment plant began pumping effluent from Winslow Township to the main CCMUA treatment facility which discharges treated effluent to the Delaware River. Eliminating infiltration of treated effluent in Winslow Township reduced groundwater recharge in the Great Egg Harbor River Basin and ultimately reducing groundwater discharge (base flow) to the Great Egg Harbor River. A study was conducted to determine the effects of eliminating the infiltration of treated effluent and reducing groundwater withdrawals from wells completed in the Kirkwood-Cohansey aquifer system on groundwater levels and base flow in the Great Egg Harbor River. The model simulates a baseline scenario with 2003-2007 withdrawals and five scenarios with different effluent infiltration conditions and 2008-2010 withdrawals using MODFLOW-2000 (version 1.18.01). This USGS data release contains all of the input and output files for the baseline scenario and five scenarios described in the associated report (https://doi.org/10.3133/sir20235002).