I can't believe nobody has replied to you. That pic looks like a biofilm, which is a a thin, slimy film of bacteria that adheres to a surface, and that can grow in any water cooling system, whether industrial pipes or a hobbyist's computer. It is probably a multi-species biofilm, meaning it comprises several different species of bacteria. It is impossible to tell without a laboratory analysis which bacteria are involved. Please Note: that biofilm might contain bacteria which could be hazardous to your health, and I hope you did not ingest any of it. It MIGHT contain something dangerous like legionella pneumophila, the bacteria that causes Legionnaire's Disease. But it probably does not. Either way you should have rinsed your skin with 99% anhydrous isopropyl alcohol, and then washed your hands thoroughly with a good bio cleanser like Hibiclens, and then rinsed all computer parts with the alcohol and then some chlorine bleach cleanser, before you flushed that biofilm reside down the drain or toilet, to avoid contaminating your local water supply, which you probably did not do. I hope you live in a place with good water treatment facilities.

Anyway, in the future, I would suggest using a copper sulfate [CuSO4(H2O)x] additive in you water to kill bacteria. See, e.g., https://www.frontiersin.org/articles...016.00626/full.

Lastly, and this is not a joke, if you have any symptoms like:

Cough.
Shortness of breath.
Fever.
Muscle aches.
Headaches.

Seek medical attention immediately.