Several water quality parameters, including inorganic nitrogens and phosphorus, were measured in groundwater from the Republican River aquifer above and below Milford Reservoir, Kansas. Ammonia and total phosphorus concentrations were considerably higher (>50%) in groundwater from the pressure relief wells along the toe of Milford Reservoir dam than from well water sampled upstream of the lake. However, the concentration of these compounds decreased to near upstream levels within 1.2 km downstream of the dam. Within the array of pressure relief wells, the concentration of ammonia was greatest in water from wells near the center of the dam. Conductivity, hardness, and alkalinity were lower, and pH was higher, in groundwater below Milford Reservoir than above it. The ratio of ammonia to total inorganic nitrogen in elutriates from Milford Reservoir sediments and water from the pressure relief wells was similar. These results suggest that water seeping out of reservoirs into underlying alluvial aquifers can leach soluble compounds, which exist in reservoir sediments, into the groundwater.