Wolli Creek is a Sydney inner-urban stream. Mostly cleared by the 1930s, 5 km of its valley were saved as a natural area by its location, its later reservation for a road, and by community action, which sent the road (M5) underground. Now being amalgamated into a 50 hectare Regional Park under National Parks and Wildlife Service management, it remains under threat. It has many diverse plant communities and a surprisingly large array of fauna, particularly birds and reptiles. Bird records exist back to the 1940s, with 100 species being sighted each year in recent times and previously unrecorded ones being added each year through monthly surveys by local volunteers. Also recorded are seventeen species of native reptile, five frog, four mammal, and ten fish species, plus a variety of feral species, although few systematic surveys have been made, mainly of a snapshot variety. Examples of each of these groups are shown or listed and the studies referenced. The gap with invertebrates is noted. The Wolli Creek Preservation Society is a local community group that has driven the protection and restoration of the habitats in the valley and the study of its interesting biodiversity.