It would seem like being sucked down that hole would be certain death. Why is there no safety fence around the hole that would prevent a person or animal that had been unfortunate enough to be pulled into its swirling vortex?

The only warning sign I can see is a 'No Fishing' sign - which obviously is being ignored.

[Not so. Read the rest of the sign. - Dave]

"Glory hole" -- you don't want to know what information you get if you "google" it!
Look here for a decent description of the descent.

If there isn't enough water in the spring runoff, they aren't able to use the Glory Hole Spillway (err, Morning Glory Ring Gate). After some dry years, they had enough water to use the gate in 2017, and for several years after. Recently, they deliberately drew down water levels so they could do maintenance on the gate.

I saw a picture of the gloryhole at flood stage and water was pouring down it at an alarming rate. The picture was captioned “Someone divided by zero.”

That hole in the water brings to mind the 1845 story by Edgar Allan Poe. Who knows what’s inside this Owyhee Reservoir hole? Possibly not what the storyteller in Poe’s tale found: "Never shall I forget the sensations of awe, horror, and admiration with which I gazed about me. The boat appeared to be hanging, as if by magic, midway down, upon the interior surface of a funnel vast in circumference, prodigious in depth, and whose perfectly smooth sides might have been mistaken for ebony, but for the bewildering rapidity with which they spun around, and for the gleaming and ghastly radiance they shot forth, as the rays of the full moon, from that circular rift amid the clouds which I have already described, streamed in a flood of golden glory along the black walls, and far away down into the inmost recesses of the abyss.”

But then, where else would it go?

I would not want to fall in there!