Wells in the Irish Dindsenchas
The Dindsenchas of Irish mythology give the physical origins, and etymological source of several bodies of water - in these myth poems the sources of rivers and lakes is sometimes given as being from magickal wells.
Connla's Well is one of a number of wells in the Irish "Celtic Otherworld". It is also termed "The Well of Wisdom", or "The Well of Knowledge", and is the mythical the source of the River Shannon. The epithet Connla's Well is known from the Dindsenchas.
Another well is described in the dindsenchas about Boann, in the text as ("Secret Well") mythologically given as the origin of the River Boyne. This well has also been referred to as Nechtan's Well, or the Well of Segais.
Some writers conflate both Nechtan's and Connla's well, making it the source of both Shannon and Boyne.
Loch Garman's mythological origin is also given in the dindsenchas - in some translations or interpretations of the text the source of the water is given as the Well of Coelrind, though this has also been rendered as port of .., or even fountain of ...
In the Dindsenchas (Sinann I) refers to a "well with flow unfailing" as the source of the Sinann (Shannon). In (Sinann II) the well is referred to as Connla's well. In the poem the well is associated with the drowning of Sinend, daughter of Lodan Lucharglan, son of Ler, of the Tuatha De Danann - giving the river its name. Hazel trees, the nuts thereof which fall into the water and feed Salmon are also mention in Sinann II.
Tipra Chonnlai, ba mór muirn,
Connla's well, loud was its sound,
|(Gwynn 1913, Sinann II, pp.292-293)|
Well of Segais
Another well is described in Dindsenchas refers to a topur diamair ("secret well") located in the Sid Nechtan. This poem tells of Boann wife of Nechtan, son of Labraid - the poem derives the origin of another river (River Boyne) from this magic well, and from the mutilation of Boann by the waters of the well.
Nechtain mac Labrada laind,
Nechtain son of bold Labraid
|(Gwynn 1913, Boand I, pp.28-29)|
This well is sometimes known as the Well of Segais (Segais means "forest"), from Boann's name in the otherwold, and the Boyne is also known as the Sruth Segsa. Other sources also refer to this well as Nechtan's Well.
In the Dictionary of Celtic Mythology (ed. James MacKillop) this well, as well as the Well of Connla are conflated, as Well of Segais, which is stated to be the source of both the River Shannon and River Boyne.
Well of Coelrind 
In the tale Garman mac Bomma Licce (Garman, son of Bomma Licce) steals the queen's crown at Temair during the drinking during the feast of Samain. He is pursued to the mouth of the River Slaney where the water's burst forth drowning him - hence giving the name of Loch Garman. In (Gwynn 1913) there is no mention of a well, the place is rendered as port Cóelrenna ("port Coelrenna"). In (Stokes 1894) the place of drowing is translated as the "well of Port Coelrenna", and the water is said to have burst forth as Garman was being drowned.. Elsewhere the place is translated "fountain [of] Caelrind".
And when the sun sets dimmed in eve, and purple fills the air,
I think the sacred hazel-tree is dropping berries there,
From starry fruitage, waved aloft where Connla's Well o'erflows;
For sure, the immortal waters run through every wind that blows.
- Gwynn 1913, Sinann I & II, pp.286-297.
- Meyer & Nutt 1895, p. 213.
- O'Curry 1883, p. 144.
- Meyer & Nutt 1895, pp. 214-5.
- Boand I, Boand II
- Gwynn 1913, Boand I & II, pp.26-.
- Monaghan, Patricia (2004), The Encyclopedia of Celtic Mythology and Folklore, "Bóand", p.50
- Ford, Patrick K. (1974), "The Well of Nechtan and "La Gloire Lumineuse"", in Larson, Gerald J.; Littleton, C. Scott; Puhvel, Jaan (eds.), Myth in Indo-European Antiquity, pp. 67–74
- Dumézil, Georges (1963), "Le puits de Nechtan", Celtica: Journal of the School of Celtic Studies (in French), 6
- MacKillop 2004, "Segais, Well of".
- Scottish Studies, 1962, p. 62
- Gwynn 1913, pp. 168-175.
- Stokes 1894, p. 430.
- O'Beirne Crowe, J. (1872), "Ancient Lake Legends of Ireland. No. II. The Vision of Cathair Mor, King of Leinster, and Afterwards Monarch of Ireland, Foreboding the Origin of Loch Garman (Wexford Haven)", The Journal of the Royal Historical and Archaeological Association of Ireland, 4th series, 2 (1): 26, JSTOR 25506605
- Greer, Mary K. (1996). Women of the Golden Dawn. Park Street Press. p. 197. ISBN 978-0-89281-607-1.
- Stokes, Whitley, ed. (1894), "The Prose Tales from the Rennes Dindshenchas", Revue Celtique (in Irish and English), 15, [Tales 33-80], pp.418-484 , e-text via CELT : text and translation
- Meyer, Kuno; Nutt, Alfred (1895), "The Voyage of Bran Son of Febal (Part 1)", Grimm Library, London: David Nut (4)
- Meyer, Kuno; Nutt, Alfred (1897), "The Voyage of Bran Son of Febal (Part 2)", Grimm Library, London: David Nut (6)
- Gwynn, Edward, ed. (1913), "The Metrical Dindshenchas Part 3", Royal Irish Academy Todd Lecture Series, Hodges, Figgis, & Co., Dublin ; Williams and Norgate, London, X , e-text at CELT : text and translation
- MacKillop, James (2004), A Dictionary of Celtic Mythology, Oxford University Press