| Cladagh River | |
| Name Other: | Swanlinbar River |
| Subdivision Type1: | Country |
| Subdivision Name1: | Republic of Ireland, United Kingdom |
| Subdivision Type2: | Province |
| Subdivision Name2: | Ulster |
| Subdivision Type3: | Region |
| Subdivision Name3: | Northern Ireland |
| Subdivision Type4: | Counties |
| Subdivision Name4: | County Cavan, County Fermanagh |
| Subdivision Type5: | Village |
| Subdivision Name5: | Swanlinbar |
| Source1 Location: | Cuilcagh Mountain, County Cavan |
| Source Confluence Location: | H143 259 Irish Grid |
| Source Confluence Coordinates: | 54.1819°N -7.7817°W |
| Source Confluence Elevation: | 265m (869feet) |
| Mouth Location: | Upper Lough Erne, County Fermanagh |
The Cladagh River (Irish: An Chlaideach or "washing river"[1]), Claddagh or Swanlinbar River, is a moderately large river which forms from a number of small streams rising in Commas townland on the south-eastern slopes of Cuilcagh Mountain, County Cavan, and flows through the village of Swanlinbar, before crossing the border into County Fermanagh and eventually flowing into Upper Lough Erne. It is ultra-oligotrophic upstream before gradually becoming oligotrophic and oligo-mesotrophic through its middle and lower reaches.
The river is a designated Special Area of Conservation.[2] The vegetation includes Ranunculetum fluitantis, Callitriche and Ranunculus peltatus. The river contains one of the largest surviving populations in Northern Ireland of the freshwater pearl mussel. The mussels, estimated to be a minimum of 10,000 in number, are confined to a 6adj=onNaNadj=on stretch of undisturbed river in the middle section.