Choin is the Scots Gaelic word for dog in its genitive case (coin), lenited because loch is a masculine noun, causing an 'h' to be placed after the 'c'.

At the head of the lake there is a broad alluvial flat, where it has been silted up for a distance of one-third mile (0.54 km) by the detritus laid down by the adjacent streams.

[6] About 1 mile (1.6 km) below the head of the lake the soundings prove a remarkable decrease in the depth, the 25 feet (7.6 m) contour-line near the Heron islands being deflected towards the centre of the loch.

The shallowing of the basin here takes place along the outcrop of very massive epidotic grits ("Green Beds") several glaciated rocky islands appearing along this line.

Beyond this outcrop there is a small shallow basin, about 41 feet (12 m) deep (Loch Dhu), floored by schistose grits, which is traversed by a fault trending north-east and south-west, with a downthrow to the east.

[6] The direction of the ice-flow during the great glaciation coincides generally with the trend of the loch, striae being found on the rocky islands as well as round the margin of the lake.