Art,
That is neat you saw a Blackwater River in Ireland. I looked it up on Wikipedia just to see where it is in the Republic of Ireland.
The Blackwater or Munster Blackwater (Irish: An Abha Mhór, The Big River) is a river which flows through counties Kerry, Cork, and Waterford in Ireland. It rises in the Mullaghareirk Mountains in County Kerry and then flows in an easterly direction through County Cork, through Mallow and Fermoy. It then enters County Waterford where it flows through Lismore, before abruptly turning south at Cappoquin, and finally draining into the Celtic Sea at Youghal Harbour. In total, the Blackwater is 169 km (105 mi) long. The total catchment area of the River Blackwater is 3,324 km2.[2] The long term average flow rate of the River Blackwater is 89.1 Cubic Metres per second (m3/s)[3]
Interestingly, there is another Blackwater River in Northern Ireland also.
The River Blackwater or Ulster Blackwater is a river in County Armagh and County Tyrone, Northern Ireland. It also forms part of the border between the United Kingdom and the Republic of Ireland, flowing between counties Tyrone and Monaghan, intersecting into Monaghan briefly. Its source is to the north of Fivemiletown, County Tyrone. The river divides County Armagh from County Tyrone and also divides County Tyrone from County Monaghan.
The Blackwater's length is 91.3 km (56.75 mi).[2] If the Blackwater's flow is measured through its path through the 30 km (19 mi) Lough Neagh and onwards to the sea via the 64.4 km (40ml) Lower Bann, the total length is 186.3 km (115.75 mi). This makes the Blackwater–Neagh–Bann the longest natural stream flow in Ulster and is longer than the Munster Blackwater.
Thank you for the encouraging words!