3D Maps.

These 3d Maps have been created from sidescan sonar data and bathymetry of Lough Corrib accumulated  since 2008.  It reveals some stunning geology, and gives us a good insight into the way the various features of the lake were formed.
Long Shallow
The Long Shallow
The Long Shallow, lying almost north / south, a remarkable glacial feature, with limestone pavements running off at right angles. Evidence of an ancient shoreline has now been found on these pavements at a depth of 15ft below current levels - indicated in orange on this bathymetric 3d illustration. The areas in blue are fairly uninteresting "deserts" of marl and fine silt.

Videos of the Limestone Pavement shoreline features can be found here
Ashford Bay.
There are two notable holes in the bay, one, a long narrow crevasse, runs from the corner of the old jetty at the mouth of the river, southwest for two hundred metres. It is 35ft deep, and generally full of fish ! very hard to catch them though.
Doon and Doon Narrows
This is looking from above the Glann shore towards Doon Narrows and Lackavrea. There is a deep hole just off Bilberry Island towards Cornamona, and another to the west of Tootoge - in the middle of the lake
Snadauns Hole
There are two deep holes near the Snadauns, one just over 100 feet deep, the other 112 feet. The bottom here is very tortured, being at the interface between granite and limestone. There are  many almost vertical dropoffs.
Bure Rock Hole

I've been told by Professor Peter Coxon at Trinity  that this kind of hole is an absolutely perfect example of what happens when high pressure water meets a very hard or immovable feature. Exactly the same phenomena can be seen on the beach as the outgoing water from a wave washes around a stone. A hole forms on the upstream side, with channels either both sides, or just one side, of the stone. Very many of the islands on the lake exhibit this, with a deep hole on the West or SW side and channels down the sides.

The glacial movement in the North lake was rather different, and this swallow tail effect can be seen at Drumsnauv and under Lackavrea Mountain. Hard areas responsible for the eroded holes have been covered in mud now, but appear to have lain in a practically NW/SE direction. Marker 159 marks a shallow that could be what is left of the feature responsible for the hole at Drumsnauv.
Drumsnauv and Lackavrea Holes
These two holes are almost identical in shape, in the north lake, one south east of Hen castle, off the point at Drumsnauv, and the other under Lackavrea. Both apparently have been caused by high pressure water during glaciation. Fogarties Rock, just north of Hen castle, is a glacial erratic left during this period, as are a string of extremely large boulders extending from Fogarties rock into the north side of Claggan Bay.
Right you can see clearly both the holes in the North Lake, and their striking similarity in shape. Sidescan data revealed a layer of aerated water in the Lackavrea hole at about 60 ft, which may be the result of water seeping into the lake under pressure.
Inishmicatreer Hole
A surprising place to find hole full of fish. It is close up to Carrickaslin and drops steeply to 55ft. There is a deep navigable channel through the rocks here up into Ballynalty Bay.
Sandy Island Hole
I've measured a point depth of 120ft here, and a deep hole extends back towards Baurisheen. This cut extends right across the lake south of Inchagoill.

Here you can clearly see the large cut that runs NE/SW across the lake. The deepest part of this cut is 155 ft, not the deepest part of the lake, but still quite impressive  for what is otherwise quite a shallow lake.

You can clearly see the effect on the geology of fast flowing water sometime in the distant past.