We pull over beside a small stand of pines and I say “we’ll only be a minute.” Half an hour later, after dragging Liam round several corners because the water “just over there” looks so inviting, we finally stop at a small natural pebble beach with scattered trees and a rocky outcrop rising behind it.

I’m fussy about my swim spots – I don’t really want other people about, there should be some trees or rocks somewhere to change behind and, ideally, it should drop to at least knee depth relatively fast – there’s nothing worse than shivering in the wind while you pick your way over sharp stones for 200 metres with your ankles turning to ice while you’re questioning exactly what you’re doing in the middle of a lake on a grey day. But this one is practically perfect – the water drops to hip height after just a few steps, that ice cold cut off rising up over your waist. It’s so clear you can see the rusty pebbles on the bottom and cold enough to shock a gasp from my chest.

I count to three and push off, screaming as I paddle and the water pretends to stop my heart. But, it turns out, I’m still alive. Once you realise you did what you didn’t think you could, everything loosens and your body feels soft and sweet as you float. I look ahead at the mountains, the V shape where they bow down to the shore, the narrow winding track along one rocky bank, the conifers shaking in the breeze.

I like to have something to aim for, so I strike out for a small tree-twisted island. I’m careful as I approach, expecting the rocks to come up shallow, but the water stays deep right to the edge. There’s a slippery plateau of rock that I climb carefully onto before ducking under the intertwined trees. As I’ve found before with random small islands I’ve swum to, it mostly seems to be covered in animal poo, so I don’t get very far. Instead, I return to the rocky shelf and sit there, hugging my knees and looking out across the water to the rising hills, the small stoney cove, the sandy footpath winding up the mountain. It’s nice to be all alone on this little outcrop.

The wind blows the water on my skin till it reddens and I slide back down into the cold water, which still clutches at my chest enough to elicit a gasp. Swimming back, a family of ducks paddle by and I take one more moment to breathe in the beautiful scene all around me and the fact that I’m a part of it.

I’m undertaking this challenge for the Alzheimer’s Society. Please sponsor me: https://www.justgiving.com/fundraising/swimbonnieswim