One of the UK agents is a pond specialist, but I lost his name. I would like to have his name. I have a pond I am working on. He knew how to use bentonite clay to patch them.
Bentonite clay may be used in some instances to repair leaking ponds. First, the pond soil should be evaluated to see if additional clay is needed. Soils with too much clay or too little will not compact well and may seep when flooded. Natural Resource and Conservation Service (NRCS) personnel at the Farm Service Office in your area should be able to look up your soils on the appropriate soil map. Some soils are suited to pond construction while others are not.
If appropriate for use, the clay should be mixed in with moist subsoils and compacted in 6 inch blankets with proper equipment to form an earthen liner that will retain water.
I have attached three publications that will explain these processes in full.
Thanks! Forrest Wynne
KSU State Extension Specialist for Aquaculture