Avon beach, as we walk and walk, turns from manicured beach huts and heaving sands, to wild waves and high cliffs and children bent double looking for fossils on the sand. There are fishermen, there are dogs, there are families and couples and children. All the world has turned out for the miraculous twinned wilderness and contentment of being near the water.

The further we walk, the quieter it is. By the time we turn to re-trace our steps, the crowds of people have ebbed away. By the time the sky is an other-worldly pink, we are alone. I say I’m going in. Liam says it’s pointless, it’s shallow, it’s almost dark. I go in anyway.

The cold is electric and deepened by the darkness. The sky’s vivid colours shift with every breath, ripening into reds and oranges. I gasp as the waves break on my stomach, count to three and launch myself. I kick, I breathe, I rinse, I wonder. I wonder at the sky, at the ever shifting, always dancing landscape of the water, at the sound of the waves as they crash and the undertow as it pulls back and the sound of the water lapping at my skin as I slide through it.

I am here, in the water. I am cold but just enough so as to know I am alive. I see the silvered crescent of the moon. My fingers and toes tingle, my heart tightens, beats, releases. Colours flood into every mouthful of air. This challenge has taken me longer than expected. It has seemed hard, seemed pointless.

I have swum in lochs and lakes, seas, rivers, lidos and tidal pools. I’ve been through crystal clear waters and roaring grey December seas. I have doubted and I have shivered and I have crammed cold fingers into gloves and gasped as hot tea hit the back of my throat and shivered with the car heater on full blast. And here I am, at the end of it all, still in the water, listening to the music it plays and marvelling at the colours in the sky. It feels no less mystical than the first time. I am here in the water. I am here beneath the moon. I am here as the pebbles hiss in the undertow. I am here, I am here, I am here.

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