Scene 1.
Nudist club, the mermaid happens upon the club. Activities director Jonni is leading the nude women through exercises, while John Leslie (Jack) and Jamie Gillis (Marty) look on. Some great porn dialogue here:
Rikki Lake: Gentlemen, you'll have to leave, it's ladies' day at the pool.
John Leslie: Well, don't you want to check my membership?
RL: [sighs] OK.
JL: [stand up, removes towel and flashes his stiffie]
RL: That's disgusting!
JL: C'mon! Don't you want to see if it's expired or not?
Leslie catches up to her in a gazebo and woos her with some more cheesy porn dialogue into various sex acts: a quick BJ, doggie, cowgirl, money shot to the tits. All the while, the mermaid has been watching, listening and learning the language. She jills off to the experience, then catches Jack's attention, but knowing no other language than sex, she only manages a few "fuck me's" and "I want to come on your face's" before disappearing back into the sea.

Here's an early view of the lovely Debi Diamond. What a whore she turned out to be!