Thanks for all your comments, will look up waterford marsh and Balls park. I have been to Broxbourne Woods, hits the mark entirely. Just wondered if there was something equivalent closer to home. Even the towpath gets a bit boring after a while!
That picture reminds me of when we were holidaying on a narrowboat in Wales. Youngest son was steering and turning the boat round when he knocked the side of the canal. (drivers end for want of a better description!) The paddle knocked him on the chest and pushed him into the water. Wish I'd had a camera on him at that time! My eldest son and I couldn't stop laughing and fortunately the water wasn't very deep so all he needed was a quick shower! Even now when I think of it it makes me laugh.