Thanks.
The river is just painted MDF with foam board banks. I've taken some pics of these sections in production. At some point I'll do a step by step blog post with paint colour notes, etc. - 'doing simple river sections on the cheap' - or something like that. In fact, the colour in the pic is a much brighter blue than the river looks in reality, it's much darker to the eye.
I've seen rivers done much better but I wanted nearly 20' of river sections with 180mm 'width of water', and I had neither the spare time (or money) to do that amount using the methods that give a better, more realistic, effect.