The Gougane Barra valley was shaped and deepened during the Pleistocene Glaciation in the period 200,000 to 10,000 years ago by a glacier which flowed from the corrie of Com Rua, at the head of the valley. This glacier flowed eastwards into the Lee Valley where is deposited extensive sheets of gravel in the Ballingeary / Inchigeela area. The lake lies in a basin carved out by the ice, and although its dark waters and dramatic situation give the impression of great depth it is in fact no deeper than 90 feet.
The valley, Com Rua (Red coum or hollow), was farmed until the 1930's, when the Irish Forestry Service (Coillte) took it over. There is much evidence of the farms in the valley as the trees were planted amongst the the high cliffs and stone ditched fields of yester year. Indeed the public toilets were built on the site of 2 farm houses whose occupants were given farms else where. The Forest Park, comprising some 350 acres, was first planted in 1938 with further planting over the succeeding years.
