Lisvane & Llanishen Reservoirs Wild Swimming

Lisvane and Llanishen are former supply reservoirs on the north edge of Cardiff, now a Welsh Government designated inland bathing water (2025) and run by Dŵr Cymru Welsh Water. You swim in a marked zone, in a booked, supervised session. Visitor centre, café, changing. Swim Wales SAFE Cymru accredited. You go because Cardiff actually has a bookable reservoir swim with a lifeguard and a ticket, and because freelance swimming here is prohibited. Underwater equipment, cold, depth. They treat unauthorised swimming as dangerous, and they are not being dramatic. If you want 90 minutes in a marked zone with a session time, this is the one.

Getting in

Pre-book organised sessions only. There is no drop-in lap. Open-water swim is about £10 for 90 minutes. A 10-session class pass is £75. Separate cheaper dipping sessions exist, plus a summer Open Water Splash for age 5+ when the water is 18°C+. That splash is not the same product as the open-water swim. Read which ticket you are buying.

There is an induction and a cold-water dipping programme as well as the full swims. If you have not done reservoir water, start there. Unauthorised swimming is prohibited. Do not turn up with a towel and hope.

Bring what a supervised open-water session usually wants: a bright hat if you have one, a towel, warm kit for after. Follow whatever the booking page asks for on the day. Sessions are 90 minutes for the main swim, which is longer than a lot of PAYG lakes.

The swim

A marked zone on a former supply reservoir. Supervised. That is the whole swimming area. Outside it there is hidden machinery. Stay in the zone. Visitor centre, café, changing — this is a proper site, not a lay-by and a gap in a fence.

Water is reservoir water: cold, deep enough to be taken seriously, designated bathing water rather than a gravel pit with buoys. The designation is recent (2025). Swim Wales SAFE Cymru accredited, which is the quality mark they are hanging the sessions on.

Dipping sessions and the summer Splash (5+, 18°C+) are how less confident swimmers and younger kids get in. The open-water swim is the longer, colder, more serious ticket. Do not mix them up in your head and then mix them up at the water.

Worth knowing

No freelance swimming. Booked supervised sessions only. Hidden machinery outside the swim zone. Cold and depth are the other reasons they police this.

The official page currently flags swimmer’s itch — cercarial dermatitis. That is a real risk they are naming, not a rumour. If you react to freshwater after a session, that is the thing to have in mind.

Weather and environment close these reservoirs. Sister venue Llandegfedd Lake at Pontypool is the same operator and the same model. It closed on 14 August 2026 for wildfire smoke. Lisvane can do the same kind of shutdown. Check before you drive up from town. If Lisvane is full, Llandegfedd is the follow-up — same booked-session-only deal, and only if it is actually open.

Gareth James / Llanishen and Lisvane Reservoirs / CC BY-SA 2.0, via Wikimedia Commons / Geograph.