That also looks like SO cord to me as we used alot of it in the "plant" mostly for hooking up temporary "but ended up permanent" stuff like big fans & portable power stations, etc. It is very tough but It is definately not kosher in that situation. It may be feed for a underwater pump of some sort as alot of them have a rubber jacket like that.
I used to run the rubber jacket a few inches past the squeeze nut & tape the heck out of it so it could not pull out like that one did............... I don't see a lock on that Box either !
I used to run the rubber jacket a few inches past the squeeze nut & tape the heck out of it so it could not pull out like that one did............... I don't see a lock on that Box either !