The definition of penalty area says:
A penalty area is:
• Any body of water on the course (whether or not marked by the Committee), including a sea, lake, pond, river, ditch, surface drainage ditch or other open watercourse (even if not containing water), and …
So, unless the course’s Committee specifically chooses to ignore the Rules of Golf by using some kind of Local Rule or marks them out of bounds, they are penalty areas.
I think one of their members once contacted one of 5e USGA rules people about this. I’ll try to find out more from him.