In the near geological past, the field used to be a highland lake, which gradually drained through karst ruptures, leaving marshy remnants in the lowest parts, around the flow of sinking river Boroštica. Those areas are home to a wet peatbog habitat unique for karst. On 1 May 2006, Ramsar included the wetland area of 3,455 hectares into its list of wetlands of international importance. Pešter is home to a number of endangered species, such as the plants Fumana bonapartei, Halacsya sendtneri and Orchis tridentata. The only nesting place of Montagu's harrier in Serbia is in this area.