There's a feeling of slight urgency and also poignancy swimming in the Dart at this time of year. You know that in a few weeks' time the water will be teeth-clenchingly cold, and the river will become unfriendly, if not hostile. So I try and snatch as many swims as I can; today we dipped at Black Pool at Hembury, an expansive oval of dark water, before swimming upstream towards the falls above it. The water was clear, the colour of cider. The reflections of the trees in the water were green, intricate and crystal clear, occasionally shuddering as we swam past.