Illawong Nature Reserve protects a section of Illawong Swamp and a small part of neighbouring Longvale Swamp which drains into Lynchs Creek, a tributary of Candlagan Creek. Although significant parts of the catchments of both of these wetlands have previously been cleared, the swamps themselves remain largely in a natural or near-natural state and provide important habitat for waterfowl.
The reserve provides habitat for a variety of other wildlife. The threatened yellowbellied glider and long-nosed potoroo have been observed near the reserve and the threatened hooded robin has been recorded on the reserve. A pair of white-bellied sea eagles maintains a nest in a large spotted gum in the reserve.
