In reply to JBfree:
It's not getting wet that I'd worry about; blue green algae, Weil's disease, dead tramps etc are all common in canals and rivers in Herts, as is the debris often hidden beneath the surface that will provide a nice vector for infection.
I've had experiences, but not generally good! One particularly lean year I 'developed' this sh*t hole, now off limits thank God. No doubt there's more of this sort of thing around though.
http://www.ukclimbing.com/logbook/crag.php?id=3453
Good luck!
