The lake is sited along a major glacial meltwater channel system where several smaller channels join the main channel. The main channel is cut in rock, is generally 80m to 90m in width and bounded by steep rock slopes which are either composed of rocky crags or draped with peat. The meltwater channel begins with an 'open intake' (250m O.D.) 1km south of Loughaveema and continues north-northwestwards as a prominent meltwater channel into the Carey Valley. The system increases greatly in size northwards.

The specific site of the lake occurs at a bend in the glacial meltwater channel where its orientation changes from north- northwest to northwest. In addition three small meltwater channels cut in rock and up to 10m to 15m in depth occur on the eastern side of the lake on the rising slopes of Cushleake Mountain. They are currently occupied by small streams. The erosional form of these channels have locally sculpted the eastern margins of the lake basin into a series of rocky crags separating the channels whereas the western margin of the feature is bounded by the continuous, steep margin of the main meltwater gash. As a result, the shape of the lake is elongated along the main channel but minor irregularities in outline and small bays are related to the position of minor channels. At the northern lake margin recent changes in the lake margin are currently being changed by peat cutting and mass movement of peat and other detritus. On the western site of the lake coarse-grained, poorly- sorted diamict and gravelly detritus of glacial origin rests on and drapes the bedrock margin along the roadside near the stream draining the lake. The detritus is composed mainly (90%) of Dalradian clasts with occasional red granite erratics.

At a maximum the water surface measures about 150m across (W-E) and 300m from north to south. Maximum water levels rise to about 217-218m O.D. and are controlled by the small stream draining to the north. This has recently been deepened and cleaned. It is lined by soliflucted glacial detritus which is not in situ.

There are two fundamental problems concerning the origin of the lake basin. First the topographic location of the lake basin could be adequately explained with reference to its location within the meltwater channel. The open intake morphology of the channel, its pattern of tributary junction angles and gradients, together with its relationship to cross-valley moraines farther north indicates it is subglacial in origin. Extensive deltas of sand and gravel within the Carey Valley farther north indicate it transported vast quantities of sediment into ponded water related to high relative sea level (McCabe and Eyles, 1988). Channel gradient also indicates ice directed drainage while thick ice covered the Loughaveema Basin. The gradient of the ice lobe was therefore from south to north in the basin. Cross-valley moraines point to a southerly ice recession during which the valley fill was trenched.

It is therefore argued that the erosion of the actual lake basin is a result of intense fluvioglacial activity as subglacial meltwater was directed northwards. The position of the overdeepened and enlarged basin with its irregular eastern margin is simply a function of an increased and abrupt input of glacial meltwater into the channel system at this site. This is supported by the three subglacial channels joining the system from the east. However these are relatively small and it is suggested that an englacial conduit draining the ice lobe concentrated high energy meltwaters to form a subglacial plunge pool. The present form of the depression and local increase in erosion of the subglacial system at this point both point to this hypothesis.

Second, the phenomena of fluctuating lake levels cannot be fully explained by the structural geology of the immediate area. As the lake lies astride a meltwater channel, floored by irregular patches of pervious, coarse-grained gravelly diamict, it is suggested that effluent seepage below the channel floor is the main process responsible for lake drainage and control of lake levels. Groundwater seepage of this type along partially buried portions of meltwater channels may be more important that hitherto realised in the control of water levels within glaciated terrain. This inference has important implications on the dispersion of environmental pollutants and water quality within larger systems (buried) in the lowlands.

The surrounding slopes are draped by peat. However, recent and current peat cuttings are rapidly degrading the visual attraction of the site in two main ways. Firstly, on the northern margins of the lake, cuttings close to lake level, are extending the lake margin into the new cuttings at times of high lake level. A muddy morass along this sector of the lake margin will result. Secondly, shallower peat extractions on the slopes above the eastern lake margin are focussing drainage leading to mass flow of peat, and incipient signs are present which indicate that slope movement will soon occur. There are also patterns of wheeled vehicles across some areas of peat which will not help the situation.