The 6-hectare (15-acre) reserve, situated on the Manning River near Taree, is a rare example of a subtropical lowland rainforest.

[3] Much of Australia's lowland sub tropical rainforest was cleared for housing and agriculture, leaving only small patches remaining, such as at Coocumbac Island.

These alluvial soils are enriched from basaltic deposits upstream at Barrington Tops and the Comboyne and Bulga plateaux.

The most obvious mammal species on the island is the grey-headed flying fox, whose numbers may reach 5,000 at certain times of the year.

[4] The ecological community on the island is known as the large fig - giant stinger tree association.