How rip currents work
Researchers in Australia have found that treacherous ocean currents are the nation's deadliest natural hazard - ahead of bushfires and floods.
Rip currents are strong, narrow channels that pull unwitting swimmers and surfers away from the shore. Some move faster than an Olympic swimmer.
Phil Mercer spoke to Dr Rob Brander, a geomorphologist at the University of New South Wales, who explained how rip currents work.
He also chatted to Chris Chapman, a lifeguard with Waverley council in Sydney.