Overview
Half Moon Bay is not a bay and there is no sand – it is a swimming platform bolted onto the Great South Wall, about halfway out towards the Poolbeg lighthouse, with ladder and slipway access straight into the Irish Sea. It is one of the most direct sea swims you can get to from the middle of Dublin, and the Half Moon club has used it as its front door since 1898.
If you are coming to swim, come near high water. At low tide there is far less to swim in, and the walk out along the wall is a fair one either way.
The swim
The platform is home to the Half Moon Swimming and Water Polo Club, which keeps a shelter and changing facilities out on the wall. You do not need to be a member to use them or to take a dip, but the club’s presence means the spot is looked after and watched over by people who know the water.
The water stays cool the year round, so a wetsuit is worth it for anything more than a quick plunge. Tides make a real difference to the depth, so check a tide chart first. The bay is sheltered and usually calm, but currents can run strong – swim with someone, especially in winter – and heed the safety notices from the Dublin Port Company, which can close the area in severe weather or during port operations.
Water quality
The Environmental Protection Agency rated the water here ‘Good’ in 2024, the same classification it held through the 2010s. That is a solid rating for a working-port location, helped by the tide flushing the spot twice a day. It comes with one firm caveat, though: do not swim after heavy rain, when overflow can push the quality down. Give it a day or two to clear.
History
The Great South Wall was finished in 1795 and was, for a time, the longest sea wall in the world, built to stop Dublin Port silting up and to give ships a safe anchorage. The Half Moon club took its name and its spot out here in 1898; its clubhouse on the wall started life as a station for an army gun battery guarding the port. The outlook has not changed much – Dublin Port working away on one side, the Poolbeg lighthouse ahead, and the open Irish Sea beyond.
Wildlife
The wall runs along the edge of South Dublin Bay, a protected area for wintering birds, so there is usually something to watch on the mudflats at low tide – ducks, waders and gulls through the colder months. Early morning is the quietest, before the swimmers and cyclists are out.
Getting there
Half Moon Bay sits at the far end of the Great South Wall, so however you come, there is a walk. The DART stations are a good way off in the city, leaving a long onward hop by bus, bike or taxi; cycling out along the wall is the pleasant option, and there is parking near Shelley Banks at the landward end. Keep to the cycle lane on the wall and give way to walkers. There is no charge and no set hours – it is an open sea-swimming spot, weather permitting.
Check the tide before you set out, skip it for a day or two after heavy rain, and bring everything you need – there are no shops or cafés at the end of the wall.