Longman Dictionary of Contemporary English
Wiktionary
n. Worthless, insignificant person or people.
WordNet
n. free-floating freshwater green algae
Usage examples of "pond scum".
Instead, he will attempt to pin us in the territory he and the pond scum have already conceded to us.
A thick pinkish mist cascaded down and was blown into the pond scum and into the rocks around its bank.
Standing beside her was a girl who should have been in a lingerie catalog, all curves and long limbs in her brief shorts and bikini top, her hair also green, but the color of summer grass rather than that of pond scum.
It might not be the best water, but the way his throat felt now he wouldn't quarrel with pond scum or even a floating corpse.
From the bottom of the pool to the sun above, the water gradually lightened from a dismal gray-brown to a pea-soup green from the pond scum that flourished under the tropical heat.
Groping through pond scum, his fingers skimmed over a curved blade.