I have this nagging feeling it's in the last mile or so of the Crouch before Battlesbridge but I was so petrified at the time that I probably didn't notice the scenery too well. Looks like pig-pens on the skyline...
Spot on, taken from Somerleyton swing bridge, there was a contingent of Dutch skiffs rowing through along with some Thames skiffs. They do some sort of exchange visit every year!