Can anyone suggest a cheap liner for a large pond?

If the pond will always be covered with water - you might want to consider a natural clay liner. Clay (bentonite) has been used in wastewater ponds for years. The only drawback is when cattail roots grow through the liner and create leaks.

Remember, the clay must be properly compacted to ensure a barrier.

What does a pond liner have to do in a nature reserve? Is there anything natural about a pond liner? Sorry guys, but if the local geology/hydrology doesn't support a pond, a pond doesn't belong in a nature reserve.

At most, you might use loam as water barrier.

What does a pond liner have to do in a nature reserve? Is there anything natural about a pond liner? Sorry guys, but if the local geology/hydrology doesn't support a pond, a pond doesn't belong in a nature reserve.

At most, you might use loam as water barrier.

I used a large tent ground sheet and that was 30 years ago and it still works,we just dug a hole the shape and size we wanted, it was large,and lined it,we got sticklebacks frogs and all sorts of creatures in the pond and my children and grand children learned all sorts of things so did their frieds,now my grandchildren have done the same thing for their children and friends, we decorated the outside with stones collected from our garden and from neighbouing gardens.