We planned to swim at Sennen, but the sea there was rough, the red flags were flying and the lifeguard designated safe area was shoulder to shoulder with surfers, swimmers and body boarders. And so we get in the water at our ‘home’ for the week, the quiet stretch of sand at Carbis bay.

It is early evening and there are only a handful of other people on the sand and none in the water. The bay is softly golden and the water curls in in white tongues, still temptingly blue. We weighed our things down a distance from the licking water and ran in.

The waves break at stomach height before you get past them and dip your shoulders in. Past the bay, the cliffs stretch away in both directions, towards the town of St Ives with its twinkling lights one one side and the wild looking cliffs of Godrevy to the other. The bay here is sheltered but the waves still rock us. I float on my back and watch my feet dipping and rising with the swell, my nail varnish the same muted turquoise as the water. The sky is pale as evening comes on and looking up at it, at the wheeling gulls and the gathering cloud, makes everything on land seem small and inconsequential.

When we get out we watch the seagulls dipping into the ever-widening stream of water that runs into the sea. The world behind them is blue with night.

I’m raising money for the Alzheimer’s Society. Please sponsor me at http://www.justgiving.com/swimbonnieswim