Main goal of presented research was the assessment of the influence of water damming in existing land reclamation systems on the surface water quality of the Upper Biebrza River catchment. Surface water quality was assessed on the concentration of BOD5, total phosphorus (TP) and total nitrogen (TN) recorded in 2014 at several monitoring points along Biebrza River and its tributaries. The upper Biebrza R. has a little (at the Sztabin gauging point even an insufficient) absorption capacity of organic pollutants and a high capacity for self-purifying and absorbing of TP and TN. The phosphorus binding capacity decreases along the river and in its upper reach it is necessary to reduce the load of P by 20% to maintain the river quality objectives. Water quality monitoring data and information about pollution sources showed high absorption capacities of TN in the monitored tributaries, which can receive an additional flux of this constituent in the amount exceeding the actual load up to several times. The absorption capacity of BOD5 and TP is lower by an order of magnitude. For Kropiwna R., it is required to reduce the load of organic components (measured as BOD5), which exceeds the requirements for the 1st quality class.