Question
I am in the middle of redoing my parents pond. because of the shape of the pond, we had to get 2 separate pieces of liner, The place we got the liner at said the best place to join would be the waterfall- would we have to seal the 2 pieces of the liner if they overlap under the waterfall? the bottom pond water level is about 1 and a half feet under the seam. the water just trickles down the waterfall. so do we still need to seal it if it over laps that much? We don't see the need to because as far as we can tell their shouldn't be anyway for water to get under the liner, but after redoing it we do not want to redo it again! I don't think it makes a difference but we left the old liner in also so its extra strong. Hope this makes sense. Thanks!

Answer
Yes, definitely seam the liner!

The best way is to rub the liners with isopropyl alcohol where you wish to join them.  Then use a 3", 2-sided seam tape between the pieces of liner.  Then use a 6", 1-sided seam tape on at least the side that will be facing the water.  You can even use 6", 1-sided tape on the side that touches the earth for added measure.

Water will find a way out and the best way you can assure this doesn't happen is to back-fill with soil and sand,pack lightly, and then use waterfall foam to seal between the rocks to create a solid pathway for the water to travel.

Lest me know of you need any more information, or if this wasn't helpful.