 The reservoir is fed by the streams which form the headwaters of the River Kent which rise to the north in Hall Cove on the southern slopes of a mountainous ridge called High Street, which is named after the nearby Roman road.It is also fed by Lingmell Gill, which drains the large corrie on the western side of Harter Fell beneath the Nan Bield Pass.After Kentmere Tarn was drained to provide agricultural land in the 1840s, water supply to the mills further downstream became erratic, and the mill owners met to plan a reservoir to regulate the flow.