The River Foyle () is a river in west Ulster in the northwest of the island of Ireland, which flows from the confluence of the rivers Finn and Mourne at the towns of Lifford in County Donegal, Republic of Ireland, and Strabane in County Tyrone, Northern Ireland. From here it flows to the city of Derry, where it discharges into Lough Foyle and, ultimately, the Atlantic Ocean. The total length of the River Foyle is . The river separates part of County Donegal from parts of both County Londonderry and County Tyrone. The district of County Donegal that borders the western bank of the River Foyle is traditionally known as the Laggan. This district includes the villages of St. Johnston and Carrigans, both of which are nestled on the banks of the River. Tributaries The Burn Dale (also known as the Burn Deele or the River Deele) flows into the River Foyle on the northern outskirts of Lifford, while the Swilly Burn flows into the Foyle near Porthall, a hamlet between St. Johnston and Lifford. St. Johnston Burn flows into the Foyle at St. Johnston, while Flushtoun Burn flows into the river on the southern outskirts of St. Johnston. Carrigans Burn flows from Port Lough, and enters the Foyle on the southern outskirts of Carrigans. Both the Burn Dennet and the Glenmornan River flow into the Foyle just to the north of Ballymagorry, entering the river a short distance to the north of Corkan Isle. Name Claudius Ptolemy's Geography (2nd century AD) described a river mouth called Ουιδουα (Widua, from PIE *widhu, 'tree') which referred to the Foyle. The Irish name is An Feabhal, which refers to Febail, father of the mythical Bran. Crossings The River Foyle is also the fastest-flowing river in Europe for its size , making the construction of bridges across it difficult. In Derry, the main crossing point, there are three bridges. The southernmost bridge, the oldest of the three, is Europe's only road traffic double-decker bridge and is officially known as the Craigavon Bridge (occasionally referred to colloquially as the Blue Bridge). The northernmost bridge, known as the Foyle Bridge, is a much larger bridge and was built to accommodate tall ships at a time when it was envisaged that the city would need to accommodate such vessels. However, this proved unnecessary as the main port was moved several miles north of the city and