The warning comes from Associated British Ports (ABP) ahead of the summer season, with warm weather over the upcoming bank holiday and half term expected to bring more people to coastal areas.

ABP, which operates ports in Newport, Barry, Cardiff, Swansea, and Port Talbot, has reminded the public that ports are busy operational environments and can be extremely dangerous places to enter the water.

Ashley Curnow, divisional port manager for ABP in Wales and the south west, said: “We want people to enjoy the summer safely, and our message is a simple one: ports are working industrial environments and can be very dangerous places to enter the water.

“Across south Wales, we are asking people to stay out of the water near port areas and to choose designated, lifeguarded locations instead, so that everyone can enjoy the coast as safely as possible.

“And if anyone does unexpectedly enter the water, it is vital to remember that cold-water shock and other hidden dangers can take effect very quickly.”

Even in calm conditions, port waters can contain strong currents, sudden drops, submerged objects, vessel movements and untreated water, creating risks that can become life-threatening very quickly.

ABP is urging people to follow the RNLI’s Float to Live advice if they unexpectedly end up in the water.

The advice is simple: resist the instinct to swim straight away and instead lean back, relax, and spread your arms and legs to help you stay afloat.

This gives your breathing time to steady and helps the effects of cold-water shock to pass.