k.. it may be me being daft, but I've taken the appropriate villager to the appropriate place for puzzle no. 6 a million times, and all he does is exactly what any other villager would do. I've put him at the edge, dropped him in... nothing different happens except the normal

Are you sure that you have all of the prerequisites for that puzzle? You need an appropriate villager and the right village tech, in addition to the body of water.

Can't try level 3 tech yet, so maybe I titled the topic appropriately! :P