As the school holidays approach, the organisations want the public to be aware of the risks linked to natural waters and to take simple steps to stay safe.
While activities in rivers, lakes, and coastal waters can be good for physical and mental health, NRW and PHW warn that natural water environments can be unpredictable and pose hidden dangers.
Hamish Osborn, environment team leader at Natural Resources Wales, said: “We know more people are looking to rivers, lakes, and coastal waters to cool off and enjoy the outdoors during periods of hot weather.
“Wales has fantastic places to connect with nature, but natural waters are different from managed swimming environments and conditions can change quickly.”
Hazards include cold-water shock, strong currents, sudden changes in depth, underwater obstacles, and blue-green algae.
While some coastal and river sites are designated bathing waters and monitored during the bathing season, most inland waters in Wales are not.
Bathing water status gives the public information about water conditions, but it does not guarantee the absence of pollution or health risks.
Water quality in rivers and lakes can change rapidly, especially after heavy rain, due to factors like land runoff, urban drainage, and storm overflow discharges.
Even clean-looking water can contain bacteria, viruses, or contaminants that could make people unwell.
Ms Osborn said: “Most rivers and lakes in Wales are not designated bathing waters, so we encourage people to make informed choices about where and when they enter the water, follow the Wild Swimming Code and take sensible steps to protect their health and safety.”
Alice Munro, consultant in environmental public health at PHW, said: “The weather, tides, currents, and water depth can all change quickly so it is important to be aware of these before you enter the water and when you are in it.
“Even in summer, the water can be extremely cold and cause cold-water shock if you get in too quickly, which can lead to drowning.”
The public is advised to choose known swimming locations, take extra care following heavy rain, cover cuts with waterproof dressings, avoid swallowing water, wash hands before eating, and shower promptly after swimming.
