scum

a layer of dirt or slime that forms on the surface of water, especially dirty water

lodo, suciedad flotante

Collocations scum on a pond

• There was scum floating on the surface of the water.

  Había lodo flotando en la superficie del agua.

a person who is very unpleasant and behaves in a way that you consider to be morally bad or criminal

canalla, basura humana

Collocations scum of society

• He's nothing but scum.

  Él no es más que basura humana.