A quick splash at the water's edge might seem like the best way to cool your tired feet when the sun's out – but chiropodist Fred Beaumont warns that if you go barefoot, it's something you could live to regret. "I always wear flip-flops when paddling, and tell my patients to do the same," he says. "A few years ago, I was bitten [see footnote] by a weever fish in shallow water – the pain was excruciating, and I couldn't run for a month afterwards."

The weever fish is one of the most poisonous in the UK. They're between 15 and 30cm long, inhabit shallow water all round the coast, and are almost impossible to spot because they lie just under the sand. "If you step on one," Beaumont says, "it injects a poisonous venom into your foot from its dorsal fin. There's no antidote. When I was bitten, the pain lasted about an hour. It was so bad, I wanted to cut my foot off."

Amputation is not, happily, the usual result of a fish bite, Beaumont adds – though extremely rare cases of cardiac failure and gangrene have been reported. If you think you have been bitten, examine the wound, he says: "A weever fish bite leaves two little puncture holes, like an adder bite."

Beaumont only sees a couple of cases of weever fish bite among his patients yearly – but you can't be too careful. "It's a good idea to check with coastguards about which beaches are particularly affected by weever fish," he says. "But flip-flops are the best way to protect your feet on the beach. Believe me – when you've been bitten once, you never let it happen again."

As told to Laura Barnett. Fred Beaumont is a chiropodist based in Whitley Bay, and a spokesman for the Institute of Chiropodists and Podiatrists: iocp.org.uk.

• ​This footnote was appended on 1 June 2011. The chiropodist quoted about his encounter with the poisonous dorsal fin of a weever fish described the experience as being "bitten". In fact when he accidentally trod on this fish he was stung. The advice is the same: wear flip-flops when paddling.