Dr. Lecter
Contributor
bus, helicopter, firetruck... again ocean diver here, I only get to see marine creatures, rocks and some debris after holiday weekends, but this is the description of quite an entertaining location.
Appears to have lots of divers coming and going... why would any one leave gear behind?
To answer your question: as an ocean diver (who occasionally dives inside wrecks, but that's neither here nor there for this purpose), I have in the past emplaced and left line out for navigating long distances where relying on compass navigation alone was not ideal. An example would be transiting a little over a quarter mile from a deeper site at 300' to a shallower wreck at 100' for deco (and staging extra bailout gas on that shallower wreck). Putting in a semipermanant line makes the drive easier, and hitting the target the first time more sure.
Can I find it via compass alone? Yes, eventually, even under bad conditions. But as a hedge, it makes sense sometimes to put line out in the ocean and leave it there. And anyone who came across a line placed/running between 300' and 150' with a reel attached to the end of it should know better than to bother it.