It's a technique that goes back to Russian peasantry (and likely before that). But it's also possible with ducks as Geoff Lawton has shown in another video. If

It's a technique that goes back to Russian peasantry (and likely before that). But it's also possible with ducks as Geoff Lawton has shown in another video. If you don't have the patience to let a bunch of ducks breed but you still want to build a pond without plastic liner you can also look into buying bentonite clay (or you may already have some clay underneath already. Just dig and find out! Just make sure to preserve the topsoil so you can replace it)