A press release just in from Waterways Ireland:
Waterways Ireland Change Advice on Travel into Limerick
Waterways Ireland is changing the advice on travel from Ardnascrusha into the Limerick Navigation due to a new service available from the ESB which provides real time information on the output from the turbines.
Boaters are advised not to travel on the Ardnacrusha to Limerick Navigation if the output from Ardnacrusha is above 20 Megawatts. The previous advice advised boaters not to travel if one turbine was operating; 1 turbine is equivalent to 20 megawatts.
The new service offers real time information on the megawatt output of Ardnacrusha by phone (tel 087-6477229) and is available 24hrs a day. Boaters are advised to contact the ESB phoneline for information on the output when making travel plans. In the event of a line failure in the real time information number, boaters can call the main Ardnacrusha number 087-9970131 for the megawatt information as well as any other information required for travel through Ardnacrusha.
This new information service is an improvement in safety for mariners who travel on the Ardnacrusha to Limerick Navigation.
Update 2018: that was in 2013. Much better information is now available here.
Irish waterways history 