Murray Cod Distribution: Why They're Absent from the Wollondilly River

The Murray cod (Maccullochella peelii) is Australia's largest freshwater fish, endemic to the Murray-Darling Basin—the vast river system spanning Queensland, New South Wales, Victoria, and South Australia. This apex predator inhabits slow-flowing, turbid rivers, creeks, and billabongs with ample woody debris for shelter. The Wollondilly River, however, lies outside this basin. Located in New South Wales' Southern Highlands, the Wollondilly flows northeast into Lake Burragorang (Warragamba Dam), part of the Hawkesbury-Nepean catchment draining to the Tasman Sea near Sydney. Its geology, hydrology, and ecology differ significantly from the Murray-Darling: cooler, clearer waters; different substrate; and a distinct fish community including Australian bass, eel-tailed catfish, and introduced trout. Murray cod have never been recorded in the Wollondilly system naturally, and stocking programs have not targeted it due to unsuitable habitat and conservation priorities focused on the species' core range. While occasional translocation attempts occur for conservation, the Wollondilly remains outside the Murray cod's natural and managed distribution.