The River Blackwater () rises in the Cuilcagh Mountains, in the townland of Gowlan, Parish of Killinagh, Barony of Tullyhaw, County Cavan. It then flows in a south-east direction and ends in Ballymagauran Lough.http://mapcarta.com/18277910 It has a fish population of brown trout, pike and perch.http://fishinginireland.info/coarse/north/mapballinamore.htm The earliest mention of the river is in poems in the Book of Magauran dating to the 1350s.