I live in N. London and the advice I gave about pumps and breaking ice, etc. is
what is generally accepted as being what you should do. I almost put in a
caveat that there may be regional differences, but thought that most people
would allow for this anyway.

With regard to diving, I think that divers are unlikely to be interested in the
microscopic variations in water temperature, where as keepers of fish in ponds
will be. Divers are more macroscopic about there water temperatures, so to
speak. The other issue is water depth. Without wanting to get all technical,
water in a shallow pond (relatively speaking) will behave differently to water
in the sea, an estuary/river, or a gravel pit that's been flooded. I really
don't want to get into a discussion about water temperature profiling of
lakes/ponds etc. Apart from anything else it' just take too long, and there'd
be little point to it all.

Happy diving/fish keeping.

Dave.