Valley Narew and park in the valley where he found the presence of 179 bird species, including 149 species of nesting - sedge warbler, Reed Bunting, warbler, reed, krzyżówkastanowiących 60% of bird species and the presence of characteristic of the valleys of the reed-swamp - spotted crake, fodder, black tern, bittern, marsh harrier. Valley Narew meets the criteria that qualify the area as a refuge for breeding birds wetland of international importance, and Europe. It is breeding region of more than 1% of the European population of at least 10 species birds, including bitterns, teal, marsh harrier, hen harrier, green, kropiatki, corncrake, and the double snipe, and the place of three breeding endangered bird species in the world - the white-tailed, corncrake and aquatic warbler. In the park there are about 40 species of mammals. Among them is small population of moose and otters and a large beaver. Water Environment the valleys are rich in fish, which are found 22 species in the park. In Park has been such the presence of 13 species of amphibians.
Valley Biebrza is unique on a European scale enclave for wetland birds. Observed here so far 263 bird species, including 185 species breeding. Of the 56 species recognized in Poland as threatened with extinction 21 nests in the Biebrza park, for example, great snipe, aquatic warbler, tern black, spotted eagle. For some birds, wetland birds Biebrza Marshes are one of the last refuges will ensure that their populations in Central Europe. For many groups of fauna data still incomplete and need to be supplemented. In the area of ​​the park were found 47 species of mammals, 12 species of amphibians, 5 species of reptiles and 37 species of fish. Invertebrate fauna is poorly known. So far recorded the presence here: 607 species of butterflies - from the 93 species of butterflies, 42 species of caddisflies, about 400 species 19 species of spiders and leeches.