The aim of the study was evaluation of ecological potential of reservoirs, once complexes of fish ponds, which are currently covered by international form of nature conservation. An effort to identify the source of reservoirs’ water supply in biogenic substances has also been undertaken. Studied dam reservoirs, included in Natura 2000 site: a Special Protection Area (SPA) called ‘Uroczysko Mosty--Zahajki’ (PLH060014). The ‘Uroczysko Mosty-Zahajki’ consists of two neighboring, not very deep reservoirs: Mosty (390 ha) and Zahajki (240 ha), located in the Hanna river’s catchment area, a tributary of the Bug and Zielawa rivers entering the Krzna river. Studied reservoirs represented moderate (reservoir Zahajki) and bad (Mosty reservoir) ecological potential. The buffer zones of Mosty and Zahajki reser-voirs were dominated by large forest complexes. The studied reservoirs are supplied with rivers and ditches contaminated with nutrients. Mosty and Zahajki reservoirs, in spite of moderate and poor ecologi-cal potential, increase the water resources of the area, have a positive impact on the circulation of water and increase the landscape and recreational values of region.