Groundwater flow and recharge in the Gellibrand Valley, Australia were studied using isotopes and geochemistry. The water table fluctuates annually, indicating recharge rates of 90-372 mm yr−1. Shallow groundwater has residence times of 100-10,000 years, while deeper groundwater is older and likely comes from higher altitudes. Local recharge occurs through the aquifer window, but most groundwater originates from the Barongarook High. The Gellibrand Valley is a discharge zone with limited local recharge. Chloride concentrations decrease over time, suggesting increased recharge rates.