Glendalough National Park Swim — September Weekend

The Glendalough September Swim Weekend is the bigger sibling of the May event, offering three distances over two days at Glendalough Upper Lake in the Wicklow Mountains. The 2026 edition runs 5–6 September: 750m and 1.5km races on Saturday, and the 3.9km Ironman distance on Sunday. Organised by Open Water Swimmer Ireland, this event has sold out every year since 2012 — it's one of the most in-demand open water swims in the country.

The Upper Lake in September is warmer than May — expect water temperatures around 14–16°C — making this the more comfortable of the two Glendalough events. The lake sits in a steep glacial valley, sheltered from wind but with dark, peaty water that limits underwater visibility. Sighting off the valley walls and mountains is the primary navigation method. The 750m and 1.5km are Saturday events, run as separate waves. Sunday is dedicated to the 3.9km (full Ironman swim distance) — a serious endurance test that loops the Upper Lake. Wetsuits are recommended but optional. The atmosphere is relaxed and well-organised, with a strong community feel among regulars. The scenery — Round Tower, mountain ridges, ancient ruins — makes this one of the most photogenic swim events in Ireland.

Registration opens 14 April 2026 at openwaterswimmer.ie. The event has sold out every year since 2012, often within days. Entry fee is approximately €55. Set a reminder and register immediately when it opens — there is no waitlist. No on-the-day entries. You can enter individual distances or the full weekend.

Glendalough is in the Wicklow Mountains, approximately 1 hour 15 minutes from Dublin via the N11 and R755. Parking at the Upper Lake is limited — arrive early, particularly on the Saturday. Most swimmers drive from Dublin on race morning or stay locally the night before. Laragh village (2 min) has a few B&Bs, and Rathdrum (15 min) and Glenmalure (20 min) have hostel and guesthouse options. Book well in advance — September in Wicklow is busy.

If you missed out on the September weekend, the Glendalough May swim (1,500m only) is the same course and often has a slightly longer registration window. For longer distances, the Gaelforce Great Fjord Swim (September) offers 750m to 8km in Killary Fjord one week later. The Swim Ireland Open Water National Championships at Lough Key (July) is the competitive alternative for swimmers chasing national-level times.