Down past a fishing boat and a tangle of nets and traps, there is a tidal pool in amongst the rocks. It sits glassy still, watching the roaring waves and the flying foam of the shoreline. A little girl and her dad are sitting on the edge, paddling and dangling feet but not swimming. But we are here to swim.

It’s slippy and the rocks are sharp, rough and barnacle encrusted, and we hobble ungracefully to the edge. Under the water the weed makes the surface as hard to grip as flowing silk. As soon as it’s shin high, I launch in. Immediately, I kick to the wall that faces the sea. Here it is deeper, deep enough to not touch, deep enough to make me want to dive down till my feet or my bum hit the bottom. And when I do, goggles on, the water is gloriously clear. I see small fish darting amongst weeds that glow and wave in the light – sap green, mossy purple, shifting glimmering red.

The clarity of the water and the stillness of its captivity is enchanting. It is a tiny pocket of a world within a world and we, just visitors, dive and splash and kick and glory in it knowing full well it will continue without a thought for us when we are gone.

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