The following change will improve the water shader for fix, by computing real depth in a cleverer way when we encounter fish.
The result is that the fishes no longer look duplicated or weird, which is much better.
It won't fix the red water. I do have an idea on how to fix that, but it would probably require re-using the renderer buffer (as we do with post-proc) and rendering an inverted skybox with some terrain alpha. We'd fix redness and we'd fix the hard-cutoff for map limits.