Which river forms part of the border between the Republic of Ireland and Northern Ireland?
A5 road (Northern Ireland) A5 road (Northern Ireland) The A5 is a major primary route in Northern Ireland. It links the city of Derry in County Londonderry with Aughnacloy, County Tyrone via the towns of Strabane and Omagh. Just south of Aughnacloy is the border with the Republic of Ireland, where the A5 meets the N2 to Dublin. Between them the A5 and N2 are the main road link between County Donegal in the Republic and Dublin. The A5 starts at a crossroads in Derry where the Craigavon Bridge meets the A2. The A5 goes south skirting the River Foyle past Prehen and through
River Blackwater (Northern Ireland) River Blackwater (Northern Ireland) 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 river enters Lough Neagh west of Derrywarragh Island and is navigable from Maghery to Blackwatertown. The small Maghery Canal enters the Blackwater south of Derrywarragh Island.