In message , Broadback
writes
Since the cold weather freezing the water my pond level has dropped
substantially. Is that likely to be natural or has it developed a leak?

I'm masochistic and have three ponds - but I love what they bring to the
garden. All have liners with a "promised" lifespan over 20 - 25 years.
They have done 8 so far. The main one has a problem similar to yours -
except that I _know_ it has a leak. During the summer I let it empty
itself until the level remained more or less constant then tracked the
"tideline" until I found the hole - made I believe by a heron. It was
more of a slash than a neat puncture. So I fixed it with the special
adhesive and a piece of spare liner. But there is now another leak - and
I don't know where. Once the ice melted the level fell considerably. I'm
considering options :-))

Regardless of what your pond is made of (liner, pre-formed "plastic",
concrete or whatever) it is a bit of a pain when it springs a leak. With
a liner you have the option of emptying it totally saving fish, plants
etc. as you go and then laying another liner inside the existing one.
But it's expensive and a lot of work.

In direct answer to your question - I would bet it is a leak rather than
natural dehydration. Good luck!
--
Gopher .... I know my place!