3. The purple flag — most tourists have no idea
Everyone knows red means danger. Almost nobody can read the purple flag — and it flies on hundreds of beaches every summer. Purple means dangerous marine life present: usually jellyfish swarms, sometimes Portuguese man-o’-war, stingrays, or sea lice. It does NOT mean sharks (that’s a cleared beach and a different protocol entirely). The trap: purple often flies on gorgeous, calm, perfect-looking days — the same warm currents that make great swimming carry the jellyfish in. See purple? Ask the lifeguard what’s in the water before your kids are in it. They love being asked.
4. Sneaker waves — the reason locals never turn their back
On certain coasts — the US Pacific Northwest most famously — the sea sends a wave every ten or twenty minutes that’s vastly larger than everything before it, surging dozens of meters further up a dry beach. They’re called sneaker waves because that’s what they do: arrive without warning, knock adults off their feet, and pull them back over log-strewn sand. The signs locals read: fresh wet sand far above the current waterline (the last sneaker’s signature), driftwood logs lying high on the beach (the sea put them there — and can float a two-ton log in ankle-deep water), and warning signs you should take literally. The rule on sneaker coasts is scripture: never turn your back on the ocean.