Concrete already provides water-proof. So we don't need the proofing qualities of clay any more. So why don't we just lay regular soil or some kind of gravel over concrete? Doing that won't damage anything but will provide a better place for fishes. What do you think?
Instead of stamping a design in the concrete, you could go the route of just spreading a coarse gravel/rock/boulder mix over the wet concrete. Press it in lightly to set it in place. This would give it the look of a river bottom. I don't think any soil would stay on the concrete if it has a slope to it. You might get some dirt to fill in between the rock that I describe above, but it will always want to settle to the bottom.
My question would be this. Can concrete really seal something waterproof? All concrete that I have seen eventually gets cracks. Cracks=leaks.
