A large share of drowning deaths are would-be rescuers. The guidance is ordered so that entering the water is the last resort, not the first instinct.
Reach. From land, with anything that extends your arm — a pole, a branch, clothing. Lie down or brace yourself so you cannot be pulled in.
Throw. Anything that floats, ideally with a line attached. A person in difficulty will hold onto it; that alone buys time.
Wade only where the bottom is firm and known, the water is shallow, and there is no current. Keep a hold on the bank or on another person.
Row — use a boat if one is there.
Swim, and tow, last. Only if you are trained, and never with a person who is still struggling: a panicking person will climb you. Take a buoyant object between you.
Call before you act if anyone else is present. 112 in the EU and EEA. Say it is a drowning, say how many, say exactly where — a bank, a bridge number, a beach marker.
Cold water. Under about 15 °C a person loses useful use of their hands within minutes, and involuntary gasping on immersion can flood the airway in seconds. Someone who has been in cold water is a casualty even if they look well, and should be kept horizontal: sudden upright movement after cold immersion can stop the heart.
Source. European Resuscitation Council Guidelines 2021, Drowning and First Aid sections, https://cprguidelines.eu/ ; WHO, Global report on drowning, https://www.who.int/publications/i/item/9789241564786