Nitrogen contamination in rural rivers may be caused due to pollutant load from plowed fields with excessive fertilization through groundwater. However there has been little information for discharge and pollutant load of groundwater into rivers. In the present study, we conducted field measurements to clarify the discharge and nitrogen flux of groundwater into the Takasakigawa River, flowing into Lake Inba-numa, with nitrogen contamination. The results indicated that: 1) nitrate concentration of groundwater was mostly higher than that of river water, and 2) discharge and nitrate flux of groundwater into the river were 73~92%, and 81~95%, respectively in the observed reach with 1.4 km in length. The source of the groundwater flowing into the Takasakigawa River were discussed using water quality data of groundwater in its watershed.
