Question: what is the worst pond scum

Daphne Ng answered on 13 Mar 2012:

To me, the worse pond scum is the kind that forms long filaments and clogs up ponds and lakes. An example is Spirogyra which is filamentous and forms thick, tangled mats in ponds. When these microalgae grow in large numbers, they become a nuisance to swimmers (imagine swimming and getting all tangled up) and boaters and other people who use the pond. Large numbers of pond scum also pose a problem to other organisms living in the pond such as fish because when these pond scum start dying and decaying, oxygen levels in the pond decrease. Hence, fish will start to die as they require the oxygen for survival.

As you can see, too much of a good thing is never a good thing!