Situated south of Zagreb, Crna Mlka is a complex of carp ponds and forest which is very important for the breeding, feeding and staging of numerous waterbird species. The alluvial wetland along the lower part of the Kupa River and its tributaries is surrounded by one of the largest complexes of alluvial oak forests in Europe. The fishponds, with their extensive water surface, marsh vegetation, and rich food resources are important for migratory and breeding waterbirds, such as ferruginous duck (Aythya nyroca) which are found in internationally important numbers. Numerous nationally threatened species and species of European concern such as the squacco heron (Ardeola ralloides) and the Eurasian curlew (Numenius arquata) have also been recorded. The wetland has a strict protection scheme as an ornithological reserve, and hunting is forbidden in the area. The fishponds are used commercially in accordance with nature conservation values. The main threat to the Site is the lack of consistent water inflow, which leads to eutrophication of the water bodies. As of 2020, a management plan was being prepared for the Site.