Measurement of the tritium content of water taken from bores along the Murrumbidgee River has yielded information concerning the permeability and flow characteristics of the underground aquifer in the Wagga area of New South Wales. The replenishment of the aquifer in time of high river levels has been established, the effect on the aquifer resulting from heavy pumping in the Wagga area has been studied, and some of the more unusual aquifer structures have been investigated.