Someone will know better than I do, but I think the cruising guides show the public moorings. There are also private moorings, which people create for their own needs - could be a small motorboat. Most owners mark them. Over time some may be maintained, others not.

Some cruisers decide to squat these moorings out of ignorance, cheapness or whatever. In the case of the You Tube captain, it appeared there was a degree of hubris.