Lough Foyle is a sealough which forms the estuary of the River Foyle in Ulster. It starts where the Foyle leaves Londonderry. It separates the Inishowen Peninsula in County Donegal, Republic of Ireland from County Londonderry in Northern Ireland.
- In the summer time, a ferry service operates between County Donegal and County Londonderry over Lough Foyle.
- The Broharris Canal was constructed in the 1820s when a cut, some two miles long on the south shore of Lough Foyle near Ballykelly was made in the direction of Limavady. It served both as a drainage channel and a navigation with goods being brought from the Port of Londonderry, and shellfish and kelp from the sand banks along the shore.
- In 1792 the four mile Strabane Canal was constructed from the tidal waters of Lough Foyle at Leck, to Strabane. The canal fell into disuse in 1962. In June 2006 the Strabane Lifford Development Commission awarded a £1.3m cross-border waterways restoration contract. The project involves the restoration of one and a half miles of canal and two locks to working order. Work is due to start on the Lough Foyle side of the canal in the summer of 2006.
At the end of the Second World War, the remnant of the German Atlantic U-boat fleet (which had been used to attack supply lines from America to Britain during the Battle of the Atlantic) were assembled in Lough Foyle and scuttled, as part of Operation Deadlight.
Flora and fauna
A survey of Lough Foyle was made between March 1937 and June 1939 by H. Blackler.  In this a map shows the distribution of certain species of algae in the lough and a full annotated list of the algae recorded along with photographs of the different sites. The list included: ‘’Cyanophyceae’’, ‘’Chlorophyceae’’, ‘’Phaeophyceae’’, ‘’Rhodophyceae’’, lichens and two species of ‘’Zostera’’. The marine algae of Lough Foyle are also included in Morton (2003).
The Royal Society for the Protection of Birds has a reserve at the lough.
The Lough Foyle Ramsar site (wetlands of international importance designated under the Ramsar Convention), is 5,447 acres in area. It was designated a Ramsar site on 2 February 1999. The site consists of the large shallow sea lough which includes the estuaries of the rivers Foyle, Faughan and Roe. It contains extensive intertidal areas of mudflats and sandflats, salt marsh and associated brackish ditches. The site qualified under Criterion 1 of the Ramsar Convention because it is a particularly good representative example of a wetland complex which plays a substantial hydrological, biological and ecological system role in the natural functioning of a major river basin located in a trans-border position. It also qualified under Ramsar criterion 2 as it supports an appreciable number of rare, vulnerable or endangered species of plant and animal.
A range of noteworthy fish species have been recorded for the Lough Foyle estuary and the lower reaches of some of its tributary rivers. These include Allis shad, Twait shad, smelt and sea lamprey, all of which are Irish Red Data Book species. Important populations of Atlantic salmon migrate through the system to and from their spawning grounds.
The site also qualified under Ramsar criterion 3 as it supports a large numbers of wintering waterfowl including internationally important populations of Whooper swan, Light-bellied Brent goose and bar-tailed godwit, as well as wildfowl species which are nationally important in an all-Ireland context, including red-throated diver, great crested grebe, mute Swan, tundra Swan|Bewick’s Swan, greylag goose, shelduck, common teal, mallard, Eurasian wigeon, common eider, and red-breasted merganser. Nationally important wader species include Eurasian oystercatcher, Eurasian golden plover, grey plover, Northern Lapwing|lapwing, red knot, dunlin, Eurasian curlew, common redshank and greenshank.
- Blackler, H. 1951. An algal survey of Lough Foyle, Northern Ireland. Proc. R. Ir. Acad. 54B(6):97 - 139
- Morton, O. 2003. The marine macroalgae of County Donegal, Ireland.. Bull. Ir. biogeog. Soc.27: 3 - 164
- Royal Society for the Protection of Birds
- "Designated and Proposed Ramsar sites in Northern Ireland". Joint Nature Conservation Committee. http://www.jncc.gov.uk/pdf/RIS/UK12014.pdf. Retrieved 2008-07-07.
- Location map: 55°7’0"N, 7°4’60"W