Cold water dipping is the latest activity being offered at Lisvane and Llanishen Reservoirs.
Described as an "invigorating and fun activity", cold water dipping is said to boost mental and physical health.
The sessions, which launch this month at Dwr Cymru Welsh Water's North Cardiff visitor attraction, include an initial compulsory two-hour induction to ensure that people learn how to dip safely.
The course, accredited by the Institute for Outdoor Learning, is followed by a guided cold-water dip in Llanishen Reservoir where water conditions are said to be perfect, with clean water and no currents or tides.
After the course and first session, participants can join the Lisvane and Llanishen Reservoirs cold-water dipping community with regular dips, meetups and events.
You can wear a wetsuit or just normal swimwear.
Activity manager for the reservoirs, Jack Bailey, said: "It's vital that this activity is carried out safely, which is why we ensure that each person who takes a dip does so as safely as possible – even if they have tried cold water dipping before."
The introduction to cold water dipping course costs £22 and takes place on: Saturday 23 March: 9am-1pm and 1pm-4pm; Saturday 30 March: 9am-1pm and 1pm-4pm; Friday 12 April: 9am-1pm and 1pm-4pm; Thursday 25 April: 5.30pm. You can book here.
Once inducted, cold water dips will be available on Saturdays and Sundays 10.45am from April.