Wildlife pond conflicting advice

Imagine what a natural pond would be like. It would have a layer of non-porous soil or rock, keeping the water in, and above that a (perhaps very deep) layer of wet soil.

The plants in your pond can't put their roots into the liner - so definitely if you want a living pond, put some soil back in. That could mean you need to dig deeper to end up with the size of pond you want. Bad luck!

First time I've heard this advice and it's set me thinking ....... wouldn't the soil need to be aquatic ie. poor soil, otherwise the water would certainly be alive, more of a pea soup than a pond. The containers used for planting aquatic plants seem to contain sufficient soil to support them, indeed in my experience they frequently require splitting because they have outgrown the space and container alloted to them.
Imho if a natural pond is desired, then the pond would be created using non-porous soil (clay?). Many of us use liners to simplify the pond making and maintaining process ........ I shall continue to put soil only in the containers my aquatics grow in.
The year before last I saw 'planting socks' for aquatic plants on sale at the Gardeners' World Live Show. In retrospect I wished I had bought some to experiment with, until I found fabric planters for the same purpose a few weeks ago at a Water Garden Centre. I am hoping they will mould themselves to the shape of my pond shelves and be less likely to fall into the deep than the plastic baskets, and may be easier to manage when plants need thinning.

Yes, Xela is right. You should use aquatic compost in a pond. This is low in nutrients so should not encourage the green algae that makes water go cloudy. You should be able to buy it at any good Garden Centre