Slimeball…a derogative term to be sure, from the modern usage, but before it was ever dragged down to the world of insults and verbal nastiness we know it for today, the scum of which we speak and the small bacteria that form them were simply the catalysts for the many beautiful colours we see in hot springs. While a whole host of thermophilic (heat-loving) microorganisms are responsible, it is the cyanobacteria, one of the more common fellows from this group, which form most of the scum. Cyanobacteria grow together in huge colonies (bacterial mats) that form the delightfully colourful scums and slimes on the sides of hot springs.
You can tell a fair bit about the water temperature and chemistry by just looking at the colour of the pools… as cyanobacteria, while not considered picky pool dwellers, do prefer one pool to another. A fear of slime actually has a term, blennophobia, a term told to me by a very savvy 12-year old -- child not scotch. The next time you hear someone flinging this insult your way, stop and tell them how attractive scum make this world.