Alfred Hitchcock Presents S05E38 - Hooked

Ray Marchand is on a fishing trip at a camp with his wife Gladys. Ray falls for and becomes involved with Nila, the young daughter of the owner of the camp. Ray plans to kill his wife so he can be with Nila. Since Gladys can't swim he will accompany her on the next fishing boat and push her off. All goes according to plan, except when the boat comes back it is Gladys who survives. She then reveals that she wants to marry Nila's dad. She'll do so, of course, after a proper mourning period.