Reeds puncturing Butyl liner

Concrete, unless you know what you're doing is tricky stuff to use if the pool is of any size, the problems get bigger the deeper it is. You're into formers and possibly re-enforcement. If there's separate pourings there's the problem of keeping it water-tight between them. But the biggest problem is the finish, it's hard to get smooth and there's no "give in it."
It also need several coats of Silglaze or whatever, to stop the lime leeching into the water.

I'm talking "fish" now. They like to rub up against "stuff" it's a way of trying to rid themselves of small parasites, (real or imagined) but with a concrete sided pool it's easy for them to scratch themselves, the mucus gets damaged and infection can set in.

 

Have to agree with Doghouse Riley, concrete ponds are great...........until you build one, often they have to be at least 6 inches thick on the walls, the base has to be thicker, and when they leak.........

That is why liners are popular, less hassle, mind you, could always build a "normal" pool and fibre glass it, last for "ever"

 

But, I put in a concrete pond! There's fish (native fish, sticklebacks), frogs, loads of newts. I put in 10 sticklebacks; now there appears to be hundreds of them! The water is HEAVING with insects.

All I did was to burn off the wizard fibre bits that were sticking out of the concrete with a blow torch. We didn't seal it but the concrete had waterproofer added to it and it was all poured via a conveyor belt in a few hours.

I'm still worried that it'll eventually leak, however, touch wood, it hasn't yet.

 

I only took over the garden last November!