I’ve always wanted to do the Great Scottish Swim. I loved the Great North Swim, so I thought the Scottish version would be fun and the wilderness of the Scottish countryside and all the lakes dotted through the Trossachs National Park made it an ideal destination. After the stress of rushing to the start this year at Windermere, we arrive two hours before my start time at Loch Lomond. Which turns out to be a good thing because I’ve managed to forget both my goggles and my towel! New pro goggles bought, I have time to get into my wetsuit and watch the warm up and departure of the wave before me with leisure.

The water is shockingly cold when I do a lap to acclimatise. Everyone around me is agreeing, wincing and gasping. “Do we get our medals now?” someone pants.

After the warm up, I join the rush into the water in the middle of the crowd. It’s easier than being at the back because there’s still a sense of momentum and there aren’t as many bodies filling the water in front. It hasn’t come to a complete standstill yet and the water is foaming between the orange capped heads and thrashing front-crawl arms.

The cold is so complete my breath is gaspy. Because it’s so icy when I dip my face in, I try and pull it out again as fast as I can. But then I can’t empty my lungs completely and so can’t fill them fully again. I flip onto my back to calm my breathing. The sky has cleared of rain and is shining blue through fluffy white clouds. A front crawler crashes into me, so I turn over and start swimming again, my breathing back to normal.

A film crew are shooting for the BBC and their camera sticks out above the splashing heads as we reach the first way-marker – a big yellow buoy. I tap the yellow canvas as I pass it. The mountains rise out of steely blue water ahead, tumbling down to the shores in a wash of green, lilac and stony blue. The line of swimmers circles round in a loop, white foam horses and bright hats stretching in colour bands up to the finish line – orange around me, a few scattered white hats from the wave before on the horizon.

You never feel alone on a swim like this, with all the bodies beating around you and the safety kayakers floating at every turn, watching closely for signs of discomfort. There are always people faster and slower than you, always someone speeding ahead and someone treading water with their head up, struggling against the cold. The age range is vast and it encourages people from all fitness types, all backgrounds, to have a try and see what they can do.

I get into a rhythm with my stroke and round the corner to the finish line, then realise I need to take it in. I keep my head up for a bit and try to comprehend the vastness of the water and the mountains, the scale that makes all these thousands of swimmers seem so small.

Lifeguards stand at the finish to help people to their feet. As I climb out, a man in front of me opens a beer given to him by a friend and drinks it right at the edge of the water. I wish I’d thought of that! With the cold and the conditions, all the people and the stunning landscape, it definitely feels like something to celebrate.

Please donate to the Alzheimer’s Society to sponsor me at https://www.justgiving.com/fundraising/swimbonnieswim