Just to clarify my post; I have put a patch of underlay on top of the lowest
part of the black butyl and then a bed of gravel on top of the centre of the
underlay (now probably better called overlay!). About 10 inches of white
underlay extends beyond the edge of the gravel and it is this that is
shining through. I cannot trim the underlay since the gravel would then too
easily get under the underlay. Also the exposed edge of the underlay is not
lying flat against the butyl - it billows up a bit. It can only be a matter
of time before some of the gravel finds its way under the 'billows' and may
then damage the butyl. Any thoughts?

cheers Davy

"Davy" wrote in message
...
Just installed a new wildlife pond. The water table is a bit high here so
I
weighted the liner down with some stone; and to protect the butyl liner I
put some underliner (overliner?) down on it first.
Filled it for the first time today and the pure white overliner shows very
distinctly. The pond is 5m by 6m and about 50cm deep.

Is it likely to improve?

Davy