Leak in the pond liner?

Question:My heavy black pond liner is leaking somewhere. In spite of filling with water, it always sinks to the same level which is about 5 inches lower than desired.

Does anyone have a way of determining where that hole would be? I intend to scrub all around the default line around the rim but, if it is a pinhole, it can be impossible to find.

any suggestions would be welcome.

Answers:
You are lucky it is not at the bottom of the pond.

Can you live with this 5 inch void. You may do more damage trying to find the hole.

See if there are sprays available that can be use to spray this 5 to 7 inch, after lowering the level more.

Even if you find the hole, I think it may be difficult to fix it. Co- adhesive (patch) may work. Was it a one piece liner? If not did it have dielectric joints.