What’s underneath fish farms in Scotland?

On the surface a fish farm can look very clean. The workers can do their very best to feed only as much as the fish eat (although mostly it’s an automated process anyway), and all kinds of other regulations can be adhered to, but fish do have to go too, and this is what you don’t see from the surface: the buildup of anaerobically rotting fish shit on the seabed.

It is claimed that the fish in a standard sized fish farm create as much sewage as a town of 65,000 people does.