 The reservoir is sometimes known as "lakes" due to its shape, which arises because it lies in not one but two river valleys - that of the Liffey and, primarily, that of the King's River.The King's River joined the Liffey at Baltiboys, at which point it was the larger flow, and when the Liffey was dammed upstream of the confluence, the King's River Valley was flooded far to the south.A ridge of land, on which the village of Valleymount lies, divides the southern part of the reservoir.