Overview
A pool you could throw a stone across is the source of the longest river in Ireland. Shannon Pot (Irish: Log na Sionna, ‘the hollow of the Shannon’) is a still, oval basin about 16 metres wide beside the R206 in Derrylahan, fringed with blackthorn and native trees. Its dark, peat-stained water wells up out of a limestone karst system and sets off on a journey of some 280 kilometres, through Blacklion, across the midland lakes and down to the Atlantic below Limerick.
Be honest with your expectations before you drive out here: this is a quiet, dark pool, not a waterfall or a gorge. The pull is the idea of it, the beginning of the Shannon, along with the mythology and the karst geology, and its place on the Cavan Way, the National Trail between Blacklion and Dowra. It’s a short stop, and the sensible plan is to fold it into a day that also takes in Cavan Burren Park a couple of minutes up the road.
Myth and legend
The most widely told version of the legend makes Síonnan the daughter of Lodan, a son of the sea god Lír. She came to the pool in search of the Salmon of Wisdom; the salmon, angered, made the water surge up and drown her, and the overflow cut the course of the river that has carried her name ever since. A second telling casts her as a granddaughter of Manannán mac Lir, reaching instead for the forbidden fruit of the Tree of Knowledge: same ending, same river.
The pool’s fame is old. The Book of Magauran (c. 1349) calls it the ‘well whence comes the Shannon, noblest stream in Inis Fáil’.
Geology and diving
Beneath the surface, the Pot is anything but still. It drains a catchment across the slopes of Cuilcagh Mountain: water from Garvagh Lough and sinkholes such as Pollnaowen and Pollboy sinks through the limestone and rises again here. In high flow it links underground to Badger Pot and Pigeon Pot in County Fermanagh, about 10 km north, part of the hidden network feeding the river.
Divers have been probing it for decades. The first exploration, in 1971, reached 9 metres before poor visibility and submerged branches turned it back. In late 2008 and early 2009 Artur Kozłowski, Alasdair Kennedy and Paul Doig widened a narrow slit in the rock and descended to a surveyed 14.6 metres, finding an unstable chamber and a strong current pushing up from a tight shaft in the floor.
The Cavan Way and around
The Pot is a natural start or finish point for the Cavan Way, which runs on to Blacklion through limestone karst, moorland and forest. The wider Cuilcagh Lakelands UNESCO Global Geopark packs a lot into a small area: the Marble Arch Caves and their guided tours, the boardwalk across the blanket bog on the Cuilcagh Boardwalk Trail, and Cavan Burren Park, with its megalithic tombs and karst pavement.
The Discovery Centre
A visitor centre is being built beside the car park. Planning permission was granted in July 2023 and construction began in July 2024, funded through Fáilte Ireland’s Platforms for Growth programme and Cavan County Council. Early hopes for a launch in early 2026 have slipped: the wet site and weather have pushed the opening to late summer 2026 at the earliest, and a dedicated company, the Shannon Pot Discovery Centre DAC, has been set up to run it alongside Cavan Burren Park. When it opens it will bring an exhibition on the pool’s geology, mythology and diving history, plus a café, a shop and an interpretive trail.
The catch for now is access. Since the works began, visits to the pool itself have been intermittent, though the Cavan Way and Cavan Burren Park stay open. Check the Geopark website before you set out.
Visiting tips
The Pot is free and open year-round in daylight. A free car park sits right beside it, with a paved, barrier-free path to a bridge over the outflow, plus a picnic area and a small playground. There are no toilets or café on site yet, so bring what you need. Beyond the paved section the ground is natural and turns muddy after rain, and the site comes into its own after a wet spell, when the outflow runs strong. Brown tourist signs mark it on the R206; there’s no public transport to the pool, so you’ll need a car. Come early for the best light and the quietest visit, and, again, check the Geopark site for access during construction.