Never thought of the Bentonite repair option. Cool.

Jim

RichToyBox wrote:
If the pond is not shifting that would cause the cracks to widen, a slurry
of bentonite put into the pond and kept mixed with an air stone will find
the leak and plug it in a few days. Once the leak has stopped, then the
pond could be pumped out and fresh water put in to get rid of the muddy
water.

If the pond is shifting causing the cracks to enlarge, or increase in
number, the best solution would be a liner, since virtually all materials
will fail as the cracks enlarge.