Algae and Scum

Algae noun - Primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves.

Scum and algae are semantically related in rootless topic. In some cases you can use "Scum" instead a noun "Algae".

Scum noun - People looked down upon as ignorant and of the lowest class.

Algae and scum are semantically related in dirt topic. You can use "Algae" instead a noun "Scum".