The most valuable natural heritage of Jastrebarsko and its surrounding area is certainly an ornithological reserve Crna Mlaka. It is located in the central part of the swamp-forest area, 11 kilometres southeast of the town Jastrebarsko.
Ponds attracted the birds, so today ornithologists on Crna Mlaka record as much as 235 bird species, out of which 98 species are related to aquatic habitats, and 74 to the forest. White-tailed eagle, lesser spotted eagle, river gulls, black storks, cormorants, herons, woodcocks and various species of ducks are just some of the many protected birds that remain here throughout most of the year. Crna Mlaka was declared in 1980 a special ornithological reserve and is under special protection. Reserve is included in the list of Ramsar Convention and in the project of Ornithologicaly important areas in Europe IBA.
A kind of trademark of Crna Mlaka is Ferruginous Duck. During summer and early autumn the largest gathering of this kind of ducks in Central Europe is exactly in Crna Mlaka – up to five thousand ducks gather!
The area of Žumberak and the Samoborsko gorje (Samobors’s surrounding hills) was designated a nature park as a protected natural resource by the Act of the Croatian parliament on 28th May, 1999. A nature park is a vast wild or partly cultivated area of countryside and/or sea, ecologically valuable on international or national level with important countryside, educational, cultural, historical, tourist and recreational resources.
Žumberak – Samoborsko gorje Nature Park covers around 333 km². Its basic aim is to protect and promote environmental and cultural beauties and resources of the area
Pokupski pool and Žumberak – Pokupski pool, depression with wet meadows, ponds and flooded forests of common oak. Biodiversity consists mostly in the number of birds species. One of the most important areas for ducks, of which the most interesting is large populations of ferruginous duck (Aythya nyroca), both species – black (Ciconia nigra) and white (White storks), and white-tailed eagle (Haliaeetus albicilla). Žumberak is a forested mountain, with intensive broad-leaved forests and hills of mosaic rural landscapes. The area has a good population of several species of woodpecker – Lesser Spotted Woodpecker (Dendrocopos minor), Middle spotted woodpecker (Dendrocopos medius), Syrian Woodpecker (Dendrocopos syriacus), Great spotted woodpecker (Dendrocopos major) and Grey-headed Woodpecker (Picus canus). Also interesting is the population of songbirds, especially Hawfinch (Coccothraustes coccothraustes).