During the Second World War, phosphate and flourspar deposits close to Doolin, Co. Clare, were investigated by the Irish Government’s mining company, Mianrai Teoranta and underground workings developed to exploit them. The flourspar deposit proved unproductive, but the phosphate deposit, which had previously been privately worked by an opencast quarry, was highly productive and was worked until 1947. The earlier opencast workings had stripped the shale covering from the bed of the Aille River, allowing it to sink into the subjacent Doolin Cave System. The existence of this open cave beneath a surface river flowing on limestone has previously been explained by reference to the heterogeneous nature of karst aquifers but can now be attributed to human activity.