Well, here in MO/AR freshwater lakes, if there are anchor chains to swim under, then, guaranteed, there is monofilament fishing line suspended beneath. If you're lucky, then silt has built up on the monofilament, and the line will be easily spotted and avoided. However, if you're not so lucky, then the monofilament will be virtually invisible, and you WILL get hung up in it. No big deal for a thoroughly trained open water diver. But, for a marginally trained open water diver, ...
The old "rules" are unambiguous--which is one reason I like/recommend/endorse them for new/newish open water divers.
I won't describe some of the "fun" stuff I was doing before I took my cavern diving course and really learned why new/newish open water divers, including moi at that time, should avoid diving in overhead environments.
rx7diver