I don't think there will be too much of a problem where carp are stocked sensibly, say 15 big fish an acre, together with other species of course that are allowed to reach a natural balance. There are literally hundreds of gravel pits throughout the country where this is the case, and darned fine fisheries they are too.
In the Trent valley there are also many many huge gravel pits which never see an angler. On many of them, angling is not allowed.
I know what I would do to create my perfect still water fishery.
I would obtain the rights on a gravel pit of at least 50 acres. I would stock it carefully on advice from experts in fishery management with tench, roach, bream, rudd and just a few big carp. I would expect such species as perch and pike to get in naturally, as they do.
I would have the gravel pit landscaped and a number of bays and headlands created. Each bay would have a small self-catering chalet with bunk beds and fridge. In each bay there would also be a punt of sorts.
There would be a ring road, around the whole fishery.
The fishery would have a tackle shop, general store for food etc, bar, restuarant and conference facilities. The idea of the fishery would be its ability to produce naturally grown on specimen fish.
If I was worth a few millions, I would certainly want to create something like this.