I think I might be misunderstanding your comment – so apologies if that’s the case – because I wasn’t suggesting the pond should be the profile shown in the picture – the opposite really.

But you’re right, if you dug the pond like this, you could change the shape afterwards by adding a clean and inert substrate like play sand. Though I’d steer clear of aquatic compost for the time being as I’m not convinced it doesn’t add unwanted nutrients – but that’s just a feeling at present as we haven’t tested it thorougly ourselves yet. My only other thought is: if you’ve got a liner in already, there might be problems with the material slipping of the slopes and into the bottom.

But you make a good point about deep water: if it’s unpolluted and you can keep it that way, it’s a good habitat for the aquatics that like…well….deeper water.

In practice, though, I’ve hardly seen any ponds where the deep areas are in good enough condition (i.e. unpolluted enough) to support the more sensitive plants that you mention. It would be wonderful if there were more ponds like this!

The other problem I see with deep areas in small ponds is that you end up with very few shallow areas because you need steep (or vertical) steps to get the depth. And then it become a trade off between deep or shallow – and as so many things like shallows I naturally go for those first.

But of course – this doesn’t work for the plants you mentions that like deeper water.

To get deep water and good shallows combined you need quite a large area – often more than people can fit in in realively small modern gardens.

But I think all this points to the fact that we’re still in the early stages of knowing how to design really good wildlife ponds in gardens. We’ve got some of the basics but there’s still a huge amount to learn.

Jeremy

As for deep areas, well here I agree that the stuff about freezing solid is quite unlikely, even here in Wales. I expect this advice has come from the specifications required to keep fish. But personally I like to grow plants that prefer deeper water like lilies and pondweeds, and it’s nice to retain some open water. In this case, deeper water in the centre is a boon.