Thanks all.

That is a great fantasy table, makes me want to build a waterfall.
It was actually pretty straightforward. The rock is all blue foam (originally roughly shaped for BSC3, but sat in a box since!), coated in thinned wall filler. The falling water was done using Everbuild Clearfix hybrid polymer adhesive (Better than silicone caulk)
This was my first attempt at this, largely as a result of this video: