Koronowski Reservoir was created in the 60-ies of XX century by soil dam on the 49.115 km of the Brda River. The main water flow was directed to east by lateral channel to the hydropower plant in Samociążek. The water flow of the Brda River in Koronowo city was stopped. "Dead" Brda on the section from the dam in Pieczyska to the hydropower plant in Samociążek is characterized by high intensity concentrated of groundwater outflows occurrence. Analyzed the intensity of groundwater outflows and the geological structure of the area between lateral channel and “Martwa” Brda valley.