Thanks everyone for the contributions. I think I will go with Sean
McKinney's advice that providing I keep the water level above that in the
surrounding ground then the pond liner will not 'hippo'. So tomorrow I will
wade in and remove the gravel stone and the 'overlay'. I will leave one
large smooth flat stone right in the middle to make sure that no gases can
get trapped under the centre of the liner.

many thanks

David

"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