In the 1840s attempts were made, as a Famine relief project, to dig a canal between Lough Corrib and Lough Mask. The river that links the two, though you can get to it at various points, including the Pigeon Hole, a mile or so north of Cong, runs underground through porous limestone for most of its length. This might have been an indication of what would happen to the canal: the porosity of the rock meant that the water just drained away, and Cong is left with a dry canal, complete with locks.

Delany was a little more subtle in his analysis of the project, giving two alternative reasons for it's abandonment, before citing the real reason.

According to Delany (A Celebration of 250 Years of Ireland's Inland Waterways - Appletree press 1992), the reasons for its abandonment were:
* The extension of railways into the West of Ireland
* Labour shortages, which increased the cost of hiring workers
* The geological makeup of the terrain through which the canal was built, which would make the canal difficult to staunch.