The lake
Lough Derg sits in the Shannon River Basin. Historically called Lough Dergart, or Loch Deirgeirt in Irish, it is a freshwater body of water. On the island of Ireland, it ranks third in size after Lough Neagh and Lough Corrib. In the Republic, it is the second largest. The shape is long and narrow. You can navigate 38.6 km (24 miles) of it. The surface covers 130 square kilometres. At its deepest point, the water drops to 36 metres. Counties Clare, Galway and Tipperary share the shores. It is the southernmost of the three great lakes of the Shannon, the others being Lough Ree and Lough Allen. Towns and villages line the banks. Portumna, Killaloe and Ballina, Dromineer, Terryglass, Mountshannon and Garrykennedy serve as bases. They make the lake work.
The name and the island
The name comes from Irish: Loch Deirgdheirc. That is one of the names of the Dagda, the father of the gods in Irish mythology. It literally means “red eye”. The lake is best known for Inis Cealtra, also called Holy Island. A pilgrim tradition has been kept there for centuries. It is a small island in the middle of the water. The whole lake has been famous for it. The water is calm enough to work. It is wide enough to feel like a sea. The light on it in the late afternoon is the best of the Shannon.
What to do
This is a cruising water. It is navigable over its full length. Cruisers and slower boats are popular here. The shore villages are the way in. Grab a coffee in Killaloe or Portumna. Walk along the shore. If the boat is running, head to the island. Downstream, close to where the lough empties into the Shannon, you will find the Doonass falls. They are the largest fall on the otherwise gently sloping river. Nearby stands the Ardnacrusha hydroelectric plant. When it was built in 1927, it was the largest in the world.
Practical
Allow a day on the lake. Spend the morning in the shore villages. Take the afternoon for the island or a cruise. Pair it with the Shannon for the full waterway day.
🧭 Route plannen