The Big Badja River, a perennial river of the Murrumbidgee catchment within the Murray–Darling basin, is located in the Monaro region of New South Wales, Australia. The river rises on the western slopes of the Great Dividing Range, north–east of Cooma at the junction of the Kybeyan and Gourock Ranges, and generally flows south and west, joined by three minor tributaries before reaching its confluence with the Numeralla River at the village of Numeralla; dropping 295 metres over its course of 32 kilometres.