Yorkshire Water is using Drowning Prevention Week to urge visitors to its reservoirs to stay safe.
From Monday the Royal Life Saving Society UK aims to raise awareness of the risks involved in swimming in open water.
Earlier this month Jonathan David Pardon, aged 38, from Huddersfield, died in Snailsden Reservoir, near Dunford Bridge, after going for a swim on a camping trip.
Geoff Lomas, of Yorkshire Water, said: “On a hot day, people can see reservoirs as a tempting place to cool down and enjoy a swim in a scenic location but they don’t appreciate just how dangerous they are.
“They can be fatal because of the chilling temperatures and the strong currents that go underneath the surface. Just a short swim can result in a tragic loss of life and we want to once again ask people to stay out of our reservoirs this summer.”
Royal Life Saving Society UK Chief Executive Di Steer added: “Young people often believe they are immortal and take unnecessary risks. We want to make them aware of dangers they may not have thought of.”