The paper discusses the discharge of highly concentrated alkaline wastewater from an industrial reservoir and its effect on surface waters. The discharge source is the Górka industrial reservoir, located in Trzebinia. The wastewater constitutes a threat to groundwater, which serves as a source of drinking water for surrounding villages. A detailed analysis of pH confirmed a high alkalinity of the tank content; the pH values were in the range of 12.5 to 13.5. Other water quality parameters (COD, sulfates, chlorides, TSS) were also very high. Initially, wastewater was discharged to the wastewater treatment plant (WWTP) in Chrzanów. Then, since the plant had refused further treatment due to operational disturbances, wastewater had to be discharged directly to the Chechło and Ropa creeks and finally to the Vistula river. A simultaneous monitoring of the water quality in these streams was provided. Wastewater discharged from the Górka reservoir was gradually diluted on its way to the Vistula river and therefore its impact on the Vistula river has been insignificant. The method turned out to be both effective and safe for the aquatic environment.