Peter wrote:
Hello all,

Our idea is to use breeze blocks (18 inches x 9 inches) three high
(circa 28 inches high in total) and 14 foot x 11 foot. We then thought
of rendering then painting the outside of the breeze blocks, leave the
inside of the breeze blocks au natural and bung in a big liner.

At that height I'd be tempted to line the inside with 1" polystyrene foam
sheet, which will both delay freezing and act as a cushion if the pond does
freeze over, relieving some of the pressure on the walls. And use plenty of
wall ties during building.