Friday 13 January. Indian officials announce the start of the world’s longest river cruise, from Varanasi to Assam via Kolkata. Environmentalists have condemned the move, arguing that increased river traffic threatens the rare Gangetic dolphin. The first time I saw one was when crossing the Ganges at Varanasi. Looking back I am not too sure why I ever started that swim. It was almost twenty-five years ago and even then the river was utterly filthy. Dead animals and humans floated downstream alongside rafts of vegetation that were tangled with rubbish. I had arranged for a boatman to row alongside in case I lost my nerve, but he was drunk by the time we left and our paths soon diverged. I began at Assi Ghat, upriver from the burning ghats, and did a rather upright breaststroke, my mouth and nose well clear of the water. It happened when I was about halfway across: a sudden disturbance of the surface dead ahead, then a pinkish grey dome appeared, a long toothy snout. The vision lasted less than a second and it did not reappear.