Do not let the hot weather tempt you into swimming in Warwickshire's lakes, quarries or other types of open water, police are asking.
The warning comes after the death of a 17-year-old in a quarry near Bishops Itchington last year.
A spokesperson for Warwickshire Police said: "Water is often a lot colder than you think, quickly draining your energy.
"The body's first reaction when entering cold water is to take an involuntary intake of breath but instead of air, water is taken in to the lungs.
"Warwickshire has a wide variety of lakes, quarries and waterways, all of which carry hidden dangers and with the summer holidays now upon us, this danger is only going to increase, with more and more people thinking that it's perfectly safe to swim in open water.
"Our advice to anyone considering going into the water is just not to do it. However, we know that people will still be tempted. So if you are out with friends and you do decide to swim, then don't drink alcohol, as this will inhibit your ability and perception of risk and will leave you unable to deal with the cold water shock.
"Stay together and look out for each other. If something does happen, call 999 immediately, do not attempt a rescue yourself."
Please visit a licensed pool or swimming baths that has a lifeguard on duty.
Click here for more advice.