Regardless, seems like never a more suitable description could be made.
Unfathomable has a less-generic meaning that, given the context, should probably be used.
That water is not fathomable, literally.
Actually, it's about 35 fathoms.
If you liked that, go to his Strid playlist and watch the one where he films underwater. Watching it, you can imagine how terrifying it would be to get sucked under water. Very creepy.
But that reading was invalid due to bubbles in the water
In a later video he goes back and checks with a better sonar, and gets the same results.