Lough Foyle in the context of "Republic of Ireland–United Kingdom border"

Ireland is an island in Northern Europe, in the north Atlantic Ocean. The island measures about 480 km (300 mi) north-south, and 275 km (171 mi) east-west, with a total area of 84,421 km (32,595 sq mi). It lies about 53°N 8°W / 53°N 8°W / 53; -8, near the western edge of the European continental shelf, part of the Eurasian Plate. Ireland is separated from the island of Great Britain by the Irish Sea to the east, and from mainland Europe by the Celtic Sea to the south. It is bounded to the north by the North Channel and to the south by St George's Channel. Ireland is the second-largest landmass in the British Isles, after Great Britain and before Lewis and Harris.

Its main geographical features include low central plains surrounded by coastal mountains. The highest peak is Carrauntoohil (Irish: Corrán Tuathail), which is 1,039 metres (3,409 ft) above sea level. The western coastline is rugged, with many islands, peninsulas, headlands and bays, while the southern and northern coasts have a smaller number of substantial sea inlets, such as Lough Foyle and Cork Harbour; no part of the land is more than around 110 km (68 mi) from the sea. The island is almost bisected by the River Shannon, which at 360.5 km (224 mi) with a 102.1 km (63 mi) estuary is the longest river in Ireland and flows south from County Cavan in the province of Ulster to form the boundary between Connacht and Leinster, and later Munster, and meet the Atlantic just south and west of Limerick. Lough Neagh is the largest of several sizeable lakes along Ireland's rivers.

The River Foyle (from Irish An Feabhal) 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 32 km (20 mi). 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.

Lough Swilly (Irish: Loch Súilí, meaning 'lake of eyes') in Ireland is a glacial fjord or sea inlet lying between the western side of the Inishowen Peninsula and the Fanad Peninsula, in County Donegal. Along with Carlingford Lough and Killary Harbour it is one of three glacial fjords in Ireland.

Londonderry Port, now operating as Foyle Port, is a port located on Lough Foyle in Northern Ireland. It is the United Kingdom’s most westerly port and an important northerly port on the island of Ireland. The current port is at Lisahally, County Londonderry, though historically the port was upriver in the city of Derry itself. It is operated by the Londonderry Port and Harbour Commissioners, whose former offices, just north of the city's walls, are now a museum.

City of Derry Airport (IATA: LDY, ICAO: EGAE), previously known as RAF Eglinton and Londonderry Eglinton Airport, is a regional airport located 7 mi (11 km) northeast of Derry, Northern Ireland. It is located on the south bank of Lough Foyle, a short distance from the village of Eglinton and 8 mi (13 km) from the city centre.

A military base until the 1950s, the airport, known locally as Eglinton Airport, had limited commercial services until the 1990s when it was redeveloped to service larger aircraft. The airport was also renamed as City of Derry Airport at that time.