The Owenmore River (, meaning "Big River") rises in the

Cuilcagh Cuilcagh () is a mountain on the border between County Fermanagh (in Northern Ireland) and County Cavan (in the Republic of Ireland). With a height of it is the highest point in both counties. It is also the 170th highest peak on the island of ...

Mountains, in the townland of Dunmakeever, civil parish of Kinawley, Roman Catholic parish of

Glangevlin Glangevlin () is a village in the northwest of County Cavan, Republic of Ireland, Ireland. It is in the townlands of Gub (Glangevlin) and Tullytiernan, at the junction of the R200 road (Ireland), R200 and R207 road (Ireland), R207 regional roads ...

, Barony of

Tullyhaw Tullyhaw (, which means 'the Territory of Eochaidh', an ancestor of the McGoverns, who lived ) is a Barony in County Cavan in Ireland. The area has been in constant occupation since pre-4000 BC. Located in the northwest of the county, it h ...

County Cavan County Cavan ( ; ) is a Counties of Ireland, county in Republic of Ireland, Ireland. It is in the Provinces of Ireland, province of Ulster and is part of the Northern and Western Region. It is named after the town of Cavan and is based on the hi ...

. It then flows in a north-west direction and ends in the

River Shannon The River Shannon ( or archaic ') is the major river on the island of Ireland, and at in length, is the longest river in the British Isles. It drains the Shannon River Basin, which has an area of , – approximately one fifth of the area of I ...

in Gowlat townlan

It has a fish population of brown trout. The Book of Magauran, dating to the 1350s, mentions an Abhainn Mór (Poem XV, stanza 9) but from the geographical description it probably means the Yellow River at Ballinamore rather than the Owenmore River. What cannot be disputed is the Owenmore River's claim to be the "true" headwaters of the River Shannon with the infant Shannon just a minor tributary of it. The Owenmore flows west for 14.5 km (9.0 mi) through the valley of Glangevlin before joining the Shannon about 3 km (2 mi) below the Shannon Pot at Lugnashinna, thus adding 11 km (7 mi) to the Shannon's overall length, taking it from 360 km (224 mi) to 372 km (231 mi).

Shannon River Basin The Shannon River Basin consists of the area containing Ireland's longest river, the River Shannon, and all of its tributaries and lakes. The official Ordnance Survey Ireland length of the Shannon from its Shannon Pot source is made up of tidal ...

References

{{coord, 54.2103, -7.9476, type:river_region:IE, format=dms, display=title Rivers of County Cavan