Complex sentence: The River Blackwater or Ulster Blackwater is a river in County Armagh and County Tyrone, Northern Ireland, that partly flows through County Monaghan, Republic of Ireland, which has its source to the north of Fivemiletown, County Tyrone.
Split into simpler sentences: The River Blackwater or Ulster Blackwater is a river in County Armagh and County Tyrone, Northern Ireland. Its source to the north of Fivemiletown, County Tyrone.