In much the same way that a leak in your car tyre never occurs at a good time, and potentially has devastating effects, a leak in your pond can have much the same impact.

Depending on how quickly you are losing water, you may be fortunate enough to have some time on your hands. Once you have identified that you are definitely losing water beyond normal evaporation it is sensible to have a plan for transferring fish into a temporary location. It is not essential to move them immediately as potentially the leak may be high in the pond liner and unlikely to threaten your fish.
Finding the leak is one significant challenge in itself but the response required to finding a leak will very much depend on the liner material itself.

For most pond owners who have a flexible liner, the choice of liner material will most likely dictate whether the necessary course of action is repair or replace. The lower budget plastic liners will most likely benefit from replacement once punctured. Repairs on such fabrics are difficult at the best of times; in situ in your back garden most likely doesn’t contribute to the criteria of ‘best of times’.

Whatever liner you have used, if you do choose to replace the liner it is obviously sensible to see if any other factors, such as a tree root, have prompted the leak, prior to fitting the replacement liner.

If you had initially chosen a more expensive butyl, or equivalent, liner the good news is that these rubber based materials are easy to repair in much the same way as a bicycle puncture.

For those who have the most durable concrete installations it would be hoped that leaks will be a rare occurrence. Fortunately, they most certainly won’t be the result of a stray root or piece of gravel but leaks are still a possibility. The down side is that a concrete repair will almost certainly require draining of the pond to safely affect. Some of the chemicals present in concrete production most certainly don’t mix well with fish.

For a pre-formed liner there is more resistance to some forms of damage than with a flexible liner. A leak does have the advantage of a fairly straightforward repair in many cases but again it is wise to understand the possible cause of the problem. Rigid liners will be exposed to stress if not properly supported and this could potentially have led to weaknesses which contributed to the leak.