Littlehampton Lifeboat is warning people heading to East Beach during the hot weather to take extra care in the water.
The South remains under a yellow heat-health alert, with temperatures expected to stay high and many families likely to head to the coast to cool off.
But swimmers are being urged not to enter the water in the first zone in front of the coastguard tower, near the river. Crews say there are very dangerous currents close to the river mouth which can quickly overwhelm even strong and experienced swimmers.
Littlehampton Lifeboat says it has already had several call-outs this season to people who have been caught out by the current and found themselves struggling in the water.
Anyone visiting East Beach is being encouraged to speak to RNLI lifeguards if they are unsure where it is safe to swim. Lifeguards are on duty at Littlehampton East Beach from 10am to 6pm throughout the summer.
The warning comes as the latest spell of warm weather brings more people to beaches, rivers and open water locations across Sussex and Hampshire.
People are also being reminded of the risk of cold-water shock. Even on a hot day, sea, river and lake water can be much colder than the air temperature. Entering cold water suddenly can cause people to gasp, breathe rapidly, panic or lose control of their movement.
Safety advice is to enter the water slowly where it is safe to do so, avoid jumping straight in, and never swim alone. Anyone who gets into trouble should try to float on their back, keep their airway clear, and call for help.
If you see someone struggling in the sea, call 999 and ask for the Coastguard.
Littlehampton Lifeboat says people should enjoy the beach, but respect the water, follow lifeguard advice and avoid areas known to have strong currents.
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