They sit at the bottom of a river below a grain silo, chewing lost corn with the catfish.
It's kind of poetic, and definitely rural (probably American - corn means one thing in the UK and another in the US). '...at the bottom of a river' is not to be taken literally: they are at a lower point on that river where the water often flows more slowly. 'River bottom' by itself is a meaningful term, a flatter place, and doesn't mean in the water or below it, either! 'Chewing lost corn with the catfish' is kind of funny, too: They (as humans?) may or may not be 'chewing it', but if they're trying to use the corn as bait to catch the catfish, the catfish aren't having any of their effort. So, it's more or less, a lost effort for the humans in catching anything, and the fish aren't doing anything to cooperate. A little overstated, maybe, but that's what I get out of it...
