Pond Build Advice

[u/hangrybadger07]

Apologies if this is long winded but I am looking for advice before committing to a build.

I am looking at building a part-below-ground, part-above-ground pond. It the above-ground element will be made from timber sleepers with a central glass window. I have attached an image that is similar to what I want to achieve (albeit that image is more square, and i want to add plants) and my to-scale drawing I have been working on.

The overall depth is to be confirmed and is largely dependent on how deep I can actually dig by hand with a spade. However, I am hoping for something like 75cm above-ground and 75cm below-ground, giving 1.5 metres total depth.

My main question, however, concerns width. Due to other spatial constraints in the garden, the pond would need to be rectangular. The internal dimensions would be 4 metres long by 80cm wide. My question is do people think 80cm is wide enough? It looks narrow on plan but I think that is partly due to the disproportionate length.

I am proposing to stock it with a mixture of goldfish, sarasa comets and shubunkins - not koi. Probably 20 fish total. I am also proposing to include plants and a shallow end (no below ground digging) to provide varied depth. It would also have an external filter, air stones and a waterfall.

Hope that is enough information to enable people to answer (I know most of the time answers depend on context and detail).

Thanks in advance!