I have a page here about the River Maigue, one of Ireland’s oldest improved navigations, and I suggest here that, as far as I can see, the navigation has never been officially closed; nor has the Office of Public Works been officially relieved of its responsibilities as navigation authority. I think, therefore, that the Maigue is still officially an open navigation, although I am open to correction on that.
Incidentally, the river’s name is locally pronounced Mag, to rhyme with bag.
In 2009 I wrote to the Powers That Be to suggest that the (much to be desired) bypass of Adare, a major bottleneck on the N21 Limerick–Tralee/Killarney road, should pass to the south of the town, thus avoiding the interference with the navigation that would undoubtedly have resulted from a northern bypass. It was no doubt the strength of my case, and a recognition of the importance of the navigation, that caused the Powers to opt for a southern bypass. A proposed link to a proposed M20 Limerick–Cork motorway may have been a minor factor in their decision: as nobody was going to build a motorway to Kerry, Adare would piggyback on the motorway to Cork.
However, An Bord Pleanála overturned the decision [PDFs available here] because the M20 proposal was withdrawn. The Irish Cattle and Sheep Farmers’ Association is pleased because it wanted a northern bypass of Adare, to be linked to a new road from Limerick to the port of Foynes; its submission on the matter is here [PDF]. A Limerick ICSA chap has a letter to the editor about the Foynes link in the current issue of the Limerick Leader, although it’s not yet available online.
Now, this proposal has the drawback that it might actually be slightly sensible: a better road to Foynes might stop people agitating for a restoration of the railway line and enable a speedy ending of port activities in Limerick, thus removing large piles of scrap from the riverside. But have the ICSA not considered the damage to the turf-boat traffic to Adare if a road bridge is added to the railway bridge downstream of Adare?