Film about fish tanks? (4)

I believe the answer is:

scum

(Other definitions for scum that I've seen before include "Film on the surface of a liquid" , "Impurities floating on surface, or despicable people" , "Impurities on water surface" , "Dirty froth" , "low life" .)

I've seen this clue in The New York 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.