page_title: River Shannon
section_title: Geography
hierarchical_section_title: River Shannon / Geography
caption_attribution_description: English: Shannon Pot; the difference between this and the previous photo is that the polarizer filter is turned 90deg and all the reflections on the water show up better
context_page_description: The River Shannon is the longest river in Ireland at 360.5 km. It drains the Shannon River Basin which has an area of 16,865 km², one fifth of the area of Ireland.
  The Shannon divides the west of Ireland from the east and south. County Clare, being west of the Shannon but part of the province of Munster, is the major exception. The river represents a major physical barrier between east and west, with fewer than thirty-five crossing-points between Limerick city in the south and the village of Dowra in the north.
  The river is named after Sionna, a Celtic goddess.
  The Shannon has been an important waterway since antiquity, having first been mapped by the Graeco-Egyptian geographer Ptolemy. The river flows generally southwards from the Shannon Pot in County Cavan before turning west and emptying into the Atlantic Ocean through the 102.1 km long Shannon Estuary. Limerick city stands at the point where the river water meets the sea water of the estuary. The Shannon is tidal east of Limerick as far as the base of the Ardnacrusha dam.
context_section_description: By tradition the Shannon is said to rise in the Shannon Pot, a small pool in the townland of Derrylahan on the slopes of Cuilcagh Mountain in County Cavan, from where the young river appears as a small trout stream. Surveys have defined a 12.8 km² (4.9 sq mi) immediate pot catchment area covering the slopes of Cuilcagh. This area includes Garvah Lough, Cavan, 2.2 km (1.4 mi) to the northeast, drained by Pollnaowen. Further sinks that source the pot include Pollboy and, through Shannon Cave, Pollahune in Cavan and Polltullyard and Tullynakeeragh in County Fermanagh, Northern Ireland. The highest point in the catchment is a spring at Tiltinbane on the western end of the Cuilcagh mountain ridge.
  From the Shannon Pot, the river subsumes a number of tributaries before replenishing Lough Allen at its head. The river runs through or between 11 of Ireland's counties, subsuming the tributary rivers Boyle, Inny, Suck, Mulkear and Brosna, among others, before reaching the Shannon Estuary at Limerick.
  Many different values have been given for the length of the Shannon. A traditional value is 390 km (240 mi). An official Irish source gives a total length of 360.5 km (224.0 mi) (being 258.1 km [160.4 mi] fresh and 102.1 km [63.4 mi] tidal). Most Irish guides now give 344 km (214 mi). Some academic sources give 280 km (170 mi), although most will refuse to give a number. The reason is that there is no particular end to a river that empties into an estuary. The 344 km length relates to the distance between Shannon Pot and a line between Kerry Head and Loop Head, the furthest reaches of the land. (It also assumes the current shipping route via Ardnacrusha, which takes 7 km (4.3 mi) off the distance.) The 280 km distance finishes where the Shannon estuary joins the estuary of the River Fergus, close to Shannon Airport. Longer distances emerged before the use of modern surveying instruments.
  At a total length of 360.5 km (224 miles), this means it is the longest river in Ireland. That the Shannon is the longest river in either Ireland or Great Britain was evidently known in the 12th century, although a map of the time showed this river as flowing out of the south of Ireland.
  There are some tributaries within the Shannon River Basin which have headwaters that are further in length (from source to mouth) than the Shannon Pot source's length of 360.5 km (224 miles), such as the Owenmore River, total length 372 km (231 mi) in County Cavan and the Boyle River, total length 392.1 km (243.6 mi) with its source in Mayo.
  The River Shannon is a traditional freshwater river for about 45% of its total length. Excluding the 102 km (63 ¹⁄₂ mi) tidal estuary from its total length of 360 km (224 mi), if one also excludes the lakes (L. Derg 39 km (24 mi), L. Ree 29 km (18 mi), L. Allen 11 km (7 mi) plus L. Boderg, L. Bofin, L. Forbes, L. Corry) from the Shannon's freshwater flow of 258 km (160 ¹⁄₂ mi), the Shannon, as a freshwater river, is only about 161 km (100 mi) long.
  Apart from being Ireland's longest river, the Shannon is also, by far, Ireland's largest river by flow. It has a long term average flow rate of 208.1 m³/s (7,350 cu ft/s) (at Limerick). This is double the flow rate of Ireland's second largest river, the River Corrib (104.8 m³/s [3,700 cu ft/s]. If the discharges from all of the rivers and streams into the Shannon Estuary (including the rivers Feale 34.6 m³/s [1,220 cu ft/s], Maigue 15.6 m³/s [550 cu ft/s], Fergus 25.7 m³/s [910 cu ft/s], and Deel 7.4 m³/s [260 cu ft/s]) are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches 300 m³/s (11,000 cu ft/s). Indeed, the Shannon is a major river by the time it leaves Lough Ree with an average flow rate (at Athlone weir) of 98 m³/s (3,500 cu ft/s), larger than any of the other Irish rivers' total flow (apart from the River Corrib at Galway).
  The Shannon Callows, areas of lowland along the river, are classified as a Special Area of Conservation.
  Settlements along the river (going upriver) include Kilrush, Tarbert, Glin, Foynes, Askeaton, S
caption: The Shannon Pot, the traditional source of the river
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