The Owenmore River (Irish: An Abhainn Mhór, meaning "big river") is a spate river in northwest County Mayo, running approximately 47 kilometres in length. It rises in the Nephin Beg Range and flows first northwards before turning westwards through Bangor Erris and then southwestwards, eventually discharging into the Atlantic Ocean via Tullaghan Bay. The river drains a large catchment of bogs, moorland, and mountains, giving it the character typical of western Irish spate rivers — subject to rapid rises and falls in water level depending on rainfall conditions in the upland catchment. With an average discharge of 14.7 cubic metres per second, flows can vary considerably.

The river passes through the town of Bangor Erris and the settlement of Bellacorick, providing some reference points along its course. The surrounding landscape is predominantly open bog and moorland, characteristic of the remote Erris peninsula in northwest Mayo.

The Owenmore is a noted fishery for salmon, grilse, and brown trout. Fishing regulations restrict angling to artificial fly only on the freshwater and part of the tidal sections, and close seasons apply — salmon and sea trout from 1 October to 31 January, and brown trout from 1 October to 14 February. Paddlers should be aware of the river's status as an active fishery when planning trips, particularly during peak salmon and trout seasons.