pond scum

American

noun

any free-floating freshwater alga that forms a green scum on water.

pond scum British

noun

a greenish layer floating on the surface of stagnant waters, consisting of various freshwater algae

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of pond scum

First recorded in 1885–90

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

B. maeuseri presumably got its dinner in a very similar way, but also more flamingo-like, rippling tentatively through the shallows, slurping up mouthfuls of lagoon water and filtering out the pond scum.

From Salon • Feb. 4, 2023

On Earth, such sediments have preserved evidence of ancient life in the form of fossilized mats of microscopic pond scum called stromatolites.

From Washington Post • Feb. 18, 2021

I try to live a clean life… and I soak in pond scum daily.

From BBC • Jul. 12, 2018

We still haven’t discovered intelligence or even believable evidence of pond scum anywhere else in the universe — not for lack of effort.

From New York Times • May 10, 2018

The stench of fish and pond scum clung to him.

From "Made You Up" by Francesca Zappia

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023