Impact of trout farms on water quality in the Marozka River (Mazurian Lakeland, Poland)

In 2004, measurements of the chemical properties of the waters of the Marozka River in the Mazurian Lakeland (northern Poland) were taken eight times in order to determine the impact two trout farms located in Szwaderki (farm A) and Kurki (farm B) had on this river. The negative impact was manifested mainly through the increased nutrient content in the river waters. The annual total phosphorus (P) load increased downstream from farm A by 19.0% and from farm B by 26.1%, while the total nitrogen (N) load was higher by 22.6% and 10.3%, respectively. In the summer, water oxygen saturation downstream from the trout farms dropped considerably whereas other physicochemical parameters did not change notably. Lake Œwiete received effluents from farm A, while Lake £anskie received those from farm B. The contribution of farm B to the total external load received by the mesotrophic Lake £anskie, which is a highly valuable ecosystem, was 12.9% total P and 5.0% total N.