With a discharge (Q) of 290ML during the day of this photo, and more than 400ML the previous day, Yabba Falls is quite a spectacle. Due to difficult access, these falls are not much known. This is one of the first published photographs of Yabba Falls. Seen here is the top plunge only, but the total fall of c500ft/165M includes a series of drops beginning with the vertical plunge into the plunge pool, rapids, chute (2nd falls) and cascades. Yabba Creek rises on the Conondale/Jimna Ranges and descends through forested areas flowing NNW towards the South Burnett catchment at first. After flowing past the forestry township of Jimna it begins to meander through a granite area that has been cleared for cattle grazing. At Old Yabba Station, this upper section of Yabba Creek then turns at right angles into hard metamorphic rocks and drops over Yabba Falls and heads towards the Mary River. Yabba Falls therefore represents the point at which the Yabba's headwaters were captured from the Burnett Catchment. Such stream captures are significant in the zoological history of the Mary River ecosystem, for the Yabba/Mary is home to the (now endangered) Mary River Cod, a species very closely related to the cod of the inland rivers of the Murray-Darling catchment.
Let me addend the following (which I have subsequently stumbled upon which supports my thesis above) from Wikipedia:
Australia provides a particularly fascinating series of examples of freshwater fish species and distributions resulting from river capture events. The formerly massive Great Dividing Range runs the length of the eastern coastline of Australia and has isolated native freshwater fish populations east and west of the range for millions of years. In the last two million years erosion has reduced the Great Dividing Range to a critical point where west-to-east river capture events have been possible. A number of native fish species that originated in the Murray-Darling river system to the west are (or were) found naturally occurring in a number of coastal systems spanning almost the entire length of the range.
None of the river capture events that allowed native fish of the Murray-Darling system to cross into and colonise these East Coast river systems seem to have formed permanent linkages. The colonising Murray-Darling fish in these East Coast river systems have therefore become isolated from their parent species, and due to isolation, the founder effect, genetic drift and natural selection, have become separate species (see allopatric speciation).
_Golden perch (Dawson-Fitzroy river system, central Queensland)._ _Eel-tailed catfish (several rivers, northern New South Wales) (However, note recent genetic research which now indicates eel-tailed catfish colonised east coast drainages in multiple colonisation events relatively recently (by evolutionary standards) and may subsequently have colonised the Murray-Darling system via an east-to-west river capture event, contrary to usual west-to-east capture events listed here.)_ _Macquarie perch (Hawkesbury-Nepean rivers, Shoalhaven River, southern New South Wales)._ _River blackfish (multiple rivers, Victoria)._ _Murray cod, whose eastern species/subspecies are:_ _Eastern freshwater cod (Clarence River system, northern New South Wales. It was also found in the Richmond River system in New South Wales but that population is now extinct.)_ _Brisbane River cod (Brisbane River system, southern Queensland. That population is now extinct, and its exact taxonomic status is not known.)_ _**The Mary River cod (Yabba Creek and the Mary River, southern Queensland.)**_ _The mountain galaxias species complex (multiple rivers, southern Queensland, New South Wales, Victoria)._
I. Stehbens MSc BA FRGS