Tell you what, I'll tell you the worst thing that happened to me on that stretch, that should put him off
It was a beautiful sunny day, we got in the boats at kerne bridge, two canadian canoes, each with one adult and one eleven yr old child in, and me in a kayak. Paddled downstream a bit and I realised that the river was quite swollen compared to how it had been on the times I'd been down that stretch before, but it was fine - the first bit of fast water was quite exhilarating after half an hour of gentle paddling, and then one of the canadian canoes got stuck on some stones. I had to climb out of my kayak and help dislodge it, they went down that bit sideways (quickest way to capsize).
It was fine for another hour so, and then a wind whipped up and it was more than a bit of a breeze. There is a corner on the river and the wind was cutting across it sharply. About 30 or more canoes (not kayaks) were stuck on the corner because every time they tried to paddle round it, their boats were blown into the opposite bank. In my kayak I had to sit watching the mayhem, paddling backwards for almost an hour and in that time only three boats managed to get round, everyone else was desperately paddling hard trying to get round the bend and ending up exactly where they started.
Then one of our canoes capsized - The adult and child had to struggle together to get the boat to the bank but it was quite steep and they only managed to get back in the boat because several kindly people gave them a hand steadying the boat and hauling them back in.
I was helpless because I couldn't leave my kayak, all I could do was watch from a distance.
After that everyone was utterly exhausted and it was another four miles back to base. Those that had capsized were also shaken up and very cold and wet.
There you go, tell him that!