Lough Derg (Shannon)

Coordinates: 52°59′N 8°19′W / 52.983°N 8.317°W / 52.983; -8.317
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Lough Derg
Loch Deirgeirt
Lough Derg is located in County Clare
Lough Derg
Lough Derg
Lough Derg (County Clare)
Lough Derg is located in County Galway
Lough Derg
Lough Derg
Lough Derg (County Galway)
Location in Ireland
Coordinates52°59′N 8°19′W / 52.983°N 8.317°W / 52.983; -8.317
TypeFreshwater lake
Primary inflowsRiver Shannon
Primary outflowsRiver Shannon
Basin countriesIreland
Max. length38.6 km (24.0 mi)
Max. width12.9 km (8.0 mi)
Surface area130 km2 (50 sq mi)
Average depth7.6 m (25 ft)
Max. depth36 m (118 ft)
Water volume0.887 km3 (0.213 cu mi)
Residence time0.15 years
Shore length1179,000 m (587,000 ft)
Surface elevation33.5 m (110 ft)
SettlementsGarrykennedy, Portumna, Killaloe & Ballina, Dromineer, Terryglass
1 Shore length is not a well-defined measure.

Lough Derg, historically Lough Dergart (Irish: Loch Deirgeirt),[1] is a freshwater lake in the Shannon River Basin, Ireland. It is the third-biggest on the island of Ireland (after Lough Neagh and Lough Corrib) and the second largest lake in the Republic of Ireland.

It is a long, narrow lake, with shores in counties Clare (south-west), Galway (north-west), and Tipperary (to the east). It is the southernmost of three large lakes on the River Shannon; the others being Lough Ree and Lough Allen. Towns and villages on Lough Derg include Portumna, Killaloe & Ballina, Dromineer, Terryglass, Mountshannon and Garrykennedy.

The lake's name evolved from the Irish Loch Deirgdheirc.[1] This was one of the names of The Dagda, the father of gods and men in Irish mythology, and literally means "red eye".[2]

Lough Derg has many islands including Inis Cealtra or Holy Island.


At its deepest, the lake is 36 m (118 ft) deep and covers an area of 130 km2 (50 sq mi).[3] Close downstream from where Lough Derg empties into the Shannon are the falls of Doonass, the largest fall on the otherwise gently sloping river. Nearby is the location of the hydroelectric power plant at Ardnacrusha, which, when built in 1927 was the world's largest.


In the nineteenth century, Lough Derg was an important artery from the port at Limerick to Dublin through the canals in the midlands of Ireland. Navigable over its full 38.6 km (24.0 mi) length, Lough Derg is today popular with cruisers and other pleasure craft, as well as sailing and fishing. The University of Limerick have an activity centre by the lake, just north of Killaloe, where there are canoes, kayaks, windsurfing, sailing dingies, and other recreations.

Lough Derg is home to an RNLI Lifeboat which is based at Dromineer, the first inland station in Ireland.[4] In June 2013, 35 people were brought to safety when a major rescue effort was undertaken after an international rowing event was hit by severe weather.[5]

Dublin City Council published a plan in 2011 for a pipeline to supply up to 350 million litres of water a day from Lough Derg to Dublin city and region. In 2016 the Parteen Basin at the south of lough was chosen as the proposed site of extraction. Water would be pumped to a break pressure tank at Knockanacree near Cloughjordan in County Tipperary and gravity fed from there to Dublin.[6][7][8][9]


A breeding pair of white-tailed eagles first nested on an island in Lough Derg in 2012. This marked a great success for the Irish reintroduction programme started in the summer of 2007.[10][11][12]

Nitellopsis obtusa, an invasive alga in the family Characeae (stoneworts), was first recorded in Ireland in this lough in 2016.[13] In 2021, invasive quagga mussels were discovered in the lake and in Lough Ree by a research team from UCD.[14]

The North-East Shore is listed as a Special Area of Conservation.[15]


See also[edit]


  1. ^ a b "Placenames Database of Ireland". Archived from the original on 14 June 2018. Retrieved 17 April 2015.
  2. ^ MacKillop, James. Myths and Legends of the Celts. Penguin, 2006. p.137
  3. ^ "Lough Derg (Lake Derg)". Archived from the original on 8 January 2000. Retrieved 31 March 2023.
  4. ^ "loughderglifeboat.com". Archived from the original on 8 February 2004. Retrieved 18 March 2020.
  5. ^ Hilliard, Mark. "Lough Derg rescue operation brings 35 ashore after rowing event". The Irish Times. Dublin. ISSN 0791-5144. Archived from the original on 22 June 2013. Retrieved 22 June 2013.
  6. ^ "Water Supply Project – Eastern and Midlands Region" (PDF). Irish Water. Archived from the original (PDF) on 8 November 2016.
  7. ^ "Warning over Shannon water extraction". RTÉ. 31 July 2008. Archived from the original on 3 January 2020. Retrieved 26 January 2020.
  8. ^ "Shannon water extraction a concern for Limerick councillors - Limerick Leader". Archived from the original on 18 July 2016. Retrieved 8 November 2016.
  9. ^ River Shannon Protection Alliance (26 October 2011). "Why we say the Dublin Region Water Supply Project is a bad scheme" (PDF). Oireachtas. Archived from the original (PDF) on 31 May 2013. Retrieved 8 November 2016.
  10. ^ "Sea eagles return to Irish nest". The Irish Times. 30 April 2012. Archived from the original on 3 May 2012. Retrieved 30 April 2012.
  11. ^ RTÉ: Rare eagle reintroduced to Ireland Archived 14 October 2012 at the Wayback Machine
  12. ^ "White-tailed Eagle". Archived from the original on 1 May 2012. Retrieved 6 April 2013.
  13. ^ Minchin, D., Boelens, R. and Roden, C. 2017. The first record of Nitellopsis obtusa (N.A.Desvaux) J.Groves (Charophyceae, Characeae) in Ireland (H9,H10). Irish Naturalists' Journal 35(2) p.105-109
  14. ^ Mainnín, Tomás O. (26 July 2021). "Invasive species flexing its 'mussels' on the Shannon". RTÉ. Archived from the original on 26 July 2021. Retrieved 26 July 2021.
  15. ^ "Conservation objectives for Lough Derg (Shannon) SPA [004058]" (PDF). National Parks and Wildlife Service. Archived from the original (PDF) on 9 July 2015.
  16. ^ Waterways Ireland ePortal Archived 2007-09-27 at the Wayback Machine