Underground water resources in the Angas-Bremer irrigation area have been used to irrigate lucerne pasture since the late 1950's. Falling water levels and rising salinities in the main aquifer, a Tertiary limestone, prompted local farmers to form an irrigation association and they approached the Department of Mines for advice in 1961. Investigations of the hydrogeology of the area have been carried out since 1967. The aquifer from which supplies are obtained is confined over most of the area, and is recharged by the ephemeral, and often brackish, Bremer and Angus Rivers. Water quality in the irrigation area is rarely better than 1400 mg/l and rises to more than 10 000 mg/l a few kilometres away from the rivers. Water balance studies have shown that an overlying unconfined aquifer contributes by downward leakage 52% of the estimated 25 000 metalitres/year extracted from the confined aquifer. This is made possible by the lack of effective confining beds between the two aquifers in the southern part of the area. The remaining withdrawals from the confined aquifer are balanced by natural recharge from the rivers on the north and north-west (22%), lateral flow of saline groundwater (14%), and introduced recharge to the aquifer from Lake Alexandrina (12%). Changes in storage are not occurring from year to year in the confined aquifer except in response to changes in irrigation demand caused by variations in annual rainfall. Depletion of the groundwater resources is not considered to be a problem. There is no transport of salt out of the system, because of groundwater flow towards the permanent cones of depression in both aquifers. The main problem facing water users is an inevitable salinity increase, cause by leakage of relatively saline water from the unconfined aquifer, recirculation of salt from irrigation water and lateral inflow of saline groundwater from adjacent areas. Downward leakage is probably most significant in the short term near irrigation wells, because of drawdown effects and the almost universal uncemented well construction. The effects will be most noticeable in the south, where areas of high salinity occur in the unconfined aquifer. Using a model which assumes perfect mixing, the confined aquifer salinity is estimated to be increasing at an approximate average annual rate of 40 mg/l. Much greater rates of salinity increase have been observed in practice, but problems or well construction make most sampling unreliable for quantitative assessment of aquifer salinity changes. The groundwater system cannot support the present level of irrigation development without continued deterioration of water quality.