The story about looking for eels at low tide is a bit like people putting their hands into holes looking for crabs at low water. The crab tends to brace it's legs and force it's back up trapping the hand between the ceiling of the hole and the top of the crab. The only way to avoid drowning may be to do a self amputation if your on your own!
I did read a story once, about an amateur diver, in America I think, went into a flooded shaft/vertical pipe to look for a leak. The area was full of obstructions under the water but the diver's arm was drawn out of the hole in the pipe, trapping him due to the pressure difference and he was on his own. He drowned, but at the post mortem, it was found he had attempted to cut his trapped arm off. This is a true story!
When scuba diving, I have seen congers - usually in day light and usually in holes in the rock but once did see one (7ft long) free swimming parallel to me in Skye I think. By the time I got hold of my buddy, who was on the other side of me, it had disappeared. They will not attack unless provoked.
Have also seen Morays in day and night time. Far easier to see them at night as they are semi nocturnal and you can semi hypnotise most fish with a diver's lamp. Once in France on a night dive I tried to grab a moray by the tail and it did not like that too much!! It whipped round and came straight for me, but fortunately it fled and did not stop to bite. It was only about 3ft long I guess but they can give a nasty bite which goes septic due to the bacteria in their mouth. Suffice to say, lesson learnt well and truly!!
As always underwater, best to look and do not touch. Then everything is happy!!
Steinbeisser