algae vs pond scum

algae

noun
  • Algal organisms viewed collectively or as a mass; algal growth. 

  • A particular kind of algae. 

pond scum

noun
  • Algae, especially when growing on the surface of a pond. 

  • Worthless, insignificant person or people. 

How often have the words algae and pond scum occurred in a corpus of books? (source: Google Ngram Viewer )