Film on a pond (4)

I believe the answer is:

scum

(Other definitions for scum that I've seen before include "Floating impurities or worthless people" , "Floating impurity layer" , "Dirt or froth on a liquid" , "Worthless man" , "Impurities on top of water or worthless people" .)

I've seen this clue in the LA Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.