River Bottom Jabbing

Here's a question. Why do people jab the river bottom?

This guy was using a pole. The people I saw doing it appeared to be homeless people. I looked up pole-poking-the-river-bottom in Google and could find no reason for doing this. They are not fishing. Are they looking for sunken treasure?

And I even saw a homeless guy who lives under a river bridge using a pickaxe! I don't think you fish using a pickaxe.

And, on another day, he was using a machete!

A mystery. A curious mystery. Maybe I'll go up to a homeless river person wielding a pole or a pickaxe or a machete and ask them why they are jabbing the river bottom. Or maybe not.