Sally wrote
I have recently moved into a house with a very large pond. The water is
brown & murky (muddy?) there are no plants growing in it & recently I
found a dead fish floating in it. The pond is approximately 150 feet
long by at most 70 feet wide & I believe is lined with puddled clay.
The house particulars stated that it was a spring fed pond ( but
knowing estate agents, that may not be the case!).

Can anyone recommend a book which might deal with large natural ponds
as all the books I've managed to find in the library & book shops seem
to relate to 6ft by 10ft man made ponds & focus on smaller plants which
wont outgrow their space.

There are a number of other fish in the pond - all a white-ish colour &
about 1 - 1 1/2 feet long - should I be feeding them, bearing in mind
the lack of vegetation in there??

As I am a complete novice, any advice would be appreciated - I wouldn't
want to lose another fish

First, identify the fish.
They sound like carp, possibly Ghost Carp a cross between Koi and ordinary
carp (why?) which are the water equivalent of pigs and root around on the
bottom and in a natural pond will cause it to always be murky by stirring up
the mud.
Alternatively they could be Grass Carp which eat anything green starting
with the best plants first.
When you have that information you need to decide if you want to keep them
or not.
Secondly, get a water test kit from a water garden specialist (Tetra are OK)
and test the water for Nitrates amongst other things, this will tell you if
the water is unhealthy. However what you do then in such a big pond goodness
knows, a pump would introduce oxygen which will help. But if it's spring fed
then that shouldn't be a problem.
Let us know.

--
Regards
Bob
In Runnymede, 17 miles West of London