As with the fauna of the area, the vegatation of the Colac district has been mostly modified beyond recognition since the arrival of white settlers.However, parts of the Stony Rises whose barenness has defied human activity are probably much as they were before white settlement. A glimpse of undisturbed vegetation can also be found at the Floating Islands Reserve in the Stony Rises. The prevalent eucalypt species of the area, the manna gum (E. viminalis), can be seen growing amongst tussocks of the large sedge Carex appressa.
The Floating Islands, in the Stony Rises, west of Colac.
Early explorers noted the dearth of shrubs and trees on the extensive grassy plains west of Port Phillip. This can be partly attributed to the heavy, alkaline, basalt-based soils as well as the exposre to wind and sun.
The lack of shrub and tree growth meant that, apart from the many basalt rocks strewn across the volcanic plains which became a resource for wall construction, the land was mostly easy to clear and the rich soils ripe for the plough and for grazing.
To the south of Colac lie the Otway Ranges, a significant pocket of cool temperate rainforest.