“Mystery balls” are “fatbergs” 

‘The first batch of debris in October were at first mistakenly called "tar balls" but were later found to contain everything from cooking oil and soap scum molecules, to blood pressure medication, pesticides, hair, methamphetamine and veterinary drugs.
Scientists said they resembled fat, oil and grease blobs - often called "fatbergs" - which are commonly formed in sewage systems.’

“Mystery balls” are “fatbergs” 

‘The first batch of debris in October were at first mistakenly called "tar balls" but were later found to contain everything from cooking oil and soap scum molecules, to blood pressure medication, pesticides, hair, methamphetamine and veterinary drugs.
Scientists said they resembled fat, oil and grease blobs - often called "fatbergs" - which are commonly formed in sewage systems.’

https://www.bbc.com/news/articles/cpql7wdz5vyo