The bed of this small lough, deep in Big Dog Forest, sits astride a faulted junction between the Glenade Sandstone Formation and a small patch (about 500m long) of the Knockmore Limestone Member of the Dartry Limestone. Chemical weathering has attacked the limestone of the western and north-western shore of the lough, creating a pronounced undercutting notch in the bank. Two small hills, also in the Knockmore Limestone north-west of the lough, show ‘Karren' features (etched ridges and grooves) on exposed rock surfaces. This association of karst features in an attractive and secluded setting gives the area great appeal.