We always visit Tarr Steps when we’re in Devon, and today being sunny it is bursting with families, dogs and children splashing in the river in rubber shoes. We walk up with the river on our right to find a quieter spot. The depth fluctuates and in many places is too shallow for more than an ankle-splashing paddle.

I go in, finally, by a bridge. The water still a little too shallow, I keep the kicking to a minimum, often using my hands to guide me over high boulders, their moss streaked tops brushing along my belly as I breathe in.

The trees bend over, a canopy of green. I’m at eye level with all the insects, with the holes on the river bank, the roots of the waving grasses and flowers. I’m smaller than everyone walking on the bank, more primitive somehow. It starts to rain and the water around me whispers with outward spilling circles.

The water is a rich caramel colour, cool but far from cold, flowing, skipping, bubbling. I am reminded that river swimming – the type of outdoor swimming I am least familiar with – is a journey. As such, it offers worlds of possibilities. For today, I hand walk back upstream to my clothes. I sit in the shallows, in a pit where the bank holds me and the water is at my waist, and I think about what swimming journeys there might be in the future, once I have finished this very nearly completed challenge.

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