Pond scum is our friend....

If it weren't for algae (Kingdom Protista) there would be no oxygen...no fish, no birds, no food chain, no us. Next time you use the term as a pejorative, think again.
Scum on the top of the turtle water dish, however, is not very useful.
"Turtle water dish scum!"
It even sounds worse!

This is actually a painting:
EVOLUTION-POND SCUM -->