This dataset contains discharge, temperature, conductivity, and ion concentration observations collected longitudinally along the Logan River. Data was collected at approximately 38 sites intermittently dispersed from the Mendon Road Aquatic Station to the Tony Grove Aquatic Station, including tributaries. Periodic data collection began in June of 2014 and continued through the summer of 2018. Measurements were made at each of the sites to capture pre/post snowmelt, summer (high ET), fall (low ET), and winter (Low ET) conditions. Discharge was measured using a SonTek Flow Tracker (velocity-area method). Temperature and conductivity were measured at each discharge site using the YSI 600 OMS. Ion samples were immediately filtered using either 0.7 um Whatman GF/F or 0.45 um Whatman Nylon Filters into acid-washed LDPE bottles and frozen (Chloride, Sulfate, Phosphate, Nitrate, Fluoride) or acidified with nitric acid (Sodium, Magnesium, Calcium, Potassium, Ammonium). All samples were transported via cooler to the lab where they were frozen until analysis. Samples were measured by ion chromatography on a Metrohm Compact IC. Standard curves were calibrated using independent NIST-traceable standards, and standards were run as unknowns to check analytical precision. GPS coordinates for each discharge site were recorded using a Garmin® GPSMAP 64. The purpose for these measurements is to determine areas of significant groundwater-surface water interaction.