The River Foyle is widely regarded as one of the finest Atlantic salmon rivers in Ireland, flowing through the northwest corner of the island where it forms part of the border between Northern Ireland and County Donegal. The river system is remarkably extensive, encompassing approximately 900 miles of prime salmon, sea trout, and brown trout fishing water across its main channel and tributaries. The Foyle drains a catchment of roughly 3,500 square kilometres, and its lower reaches transition into a dynamic tidal estuary where freshwater meets the saltwater of Lough Foyle — a mixing zone that creates a rich and diverse aquatic environment. The village of St Johnston on the County Donegal bank is a well-known fishing settlement along the river, and the system has attracted anglers for centuries, with fishing rights historically managed under royal charter before transitioning to modern cross-border governance.