Evening out the folds

This is done best on a warm sunny day, to make the liner more malleable.

Place the pond liner over the underlay, with excess liner evenly spread around the edge. It's easier to stand in the hole to push the liner into the corners, but take your shoes off first to avoid the risk of puncture.

Start filling the pond with water while easing the liner into folds and pleats evenly around the hole. Fill right to the brim. Then trim the liner and underlay, leaving enough to fold over the exterior plywood strip and anchor down. Backfill the gap on the outside edge with soil to trap the liner and underlay against the plywood strip. Tamp down the soil firmly.