If your pond has a butyl liner, leaks may be caused by punctures. The easiest way to repair this is with double-sided adhesive tape which can be used to secure a patch of butyl liner over a hole.

Flex Seal "stops leaks fast and is the easy way to coat ... and launched the boat in our lab "pond." We also used Flex Seal on a copper pipe with drilled holes of different sizes, on an unsealed ...