See the latest comment where Paula asks:
‘What’s the best way to enlarge my pond without disturbing it? I thought to make two ponds with a bog area between the two? Any other ideas?‘
Well, actually I don’t have a better suggestion and this is pretty much exactly what I’d do too.
Indeed, unless the pond is dug into a natural substrate, like clay, it’s probably the only practical way of extending the water area in a garden.
The bog area would be good – though not essential, as you don’t need a physical water connection between the ponds for them to work as a unit. Plenty of animals and plants using the ponds will be able to move between them without a wetland connection. One thing to be careful of would be to make sure the bog garden wasn’t a source of nutrients – make it with very low nutrient substrate (and avoid using peat aka destroyed wetland).
My only other thought is why stop at two!