Now and Forever (1983)

Man and woman (not his wife) have sex on floor very early in movie, fully clothed (!), lots of moaning. Man lies to his wife about not being involved in adultery. Shower scene with man and woman, but pretty tame and nothing close to nudity. Woman goes swimming in a pond, apparently skinny-dipping. We see her back, and a diffused view from above through the water, so details highly obscured -- can't really tell if she's actually naked or if she is wearing a flesh-colored suit. (Knowing Cheryl Ladd, she probably wasn't actually naked.)