This Basin has a large central/southern area of moderate to steep forested-hills of the Otway Ranges, with all the larger streams draining from its southern slopes into the sea, east and west of Cape Otway. The remainder of the Basin is all cleared farmland. Soils are sedimentary in origin except for small areas of volcanic rock north of Torquay and around Lake Purrumbete. Annual rainfall is 1,000 to 2,000 mm in the Otway Ranges.
The remainder of the basin receives 700-1,000 mm except around Torquay which receives 500-700 mm. There are two large rivers, the Gellibrand and the Curdies. Other waterways are small streams flowing a short distance from forested hills to the sea. They have high gradients and are characterized by cascades and rapids, with coarse substrates and small estuaries. The high rainfall in the forested areas ensures a reliable flow regime in most waterways and particularly in the Gellibrand River. The streams flowing through native forest carry self-sustaining populations of brown trout and provide very scenic fishing environments. Some waters in this Basin are commercially fished for short-finned eel.
Freshwater Fish in the Basin
- (Large fish): Australian grayling, estuary perch, river blackfish, and short-finned eel.
- (Small fish): Tasmanian mudfish, Australian smelt, climbing galaxias, common galaxias, congoli, flathead gudgeon, mountain galaxias, pouch lamprey, trout galaxias and southern pigmy perch.
- Atlantic salmon, brown trout, chinook salmon, eastern gambusia, European carp, goldfish, rainbow trout, redfin and tench.
Native species in bold are protected in this Basin. Introduced species in bold are declared noxious.
Short-finned eel is the most widespread species. Three species of galaxias are abundant with many creeks containing all three. The only other Basin where this occurs in is the Bunyip Basin, in creeks on the Mornington Peninsula. Australian grayling are quite widespread but never in large numbers. It is interesting that the fauna of the short coastal streams differs from that of the adjacent Barwon or Gellibrand River systems. For example river blackfish, Australian smelt, mountain galaxias and southern pygmy perch are not found in any coastal creeks from Anglesea to Cape Otway. Instead the fish fauna in these streams resembles that in the eastern coastal streams of Mornington Peninsula and in Tasmania.
Rivers in the Otway region contain a valuable assemblage of mainly native freshwater fish. Communities of three species of galaxias are uncommon and of high conservation value. There is only one widespread introduced fish, the brown trout. Large numbers of brown trout of good angling size were present at 52 sites in comprehensive surveys in this Basin from 1983 to 1988. For this reason only two waters are now regularly stocked.