Would anyone like to comment on the imagery in this poem?:?

I appreciate your poem for the effort it took. But I think you're showing us a first draft. There are word choices and phrases in this I suspect you're not entirely satisfied with. A poem this simple should revel in its simplicity (be even simpler yet), but also try harder for a pithy ending, or a twist... a payout of some kind. The imagery is pretty good but nothing new or surprising. That "sudden splash" has potential... (A heron? I hoped...)

It has great imagery, but I sense beneath the surface, something darker needing to be tapped, some repressed unconscious feeling or thought...

It was all too serene...until I felt the jolt in the end...imagining someone jumped in to commit suicide!

Was that the intent?

I can identify with the imagery having spent much time on rivers. I like the feel of the poem.

There ya go

I can certainly picture it in my minds eye, very good,

I set upon a rock. The sun to my back. There it reflects of the sea in the flashes of polished nickle. With chum below me at my feet. Harpoon in my hand. I strike down at a silver flash. In the sea I do go to press that flash to the bottom. A great Tuna do I have. I drag that to shore. My cell phone do I take & say start the fires. For Tuna will we have tonight washed down with fine tropical rhum. You can not see down into the depths threw the reflection of the sun deep into the water to see what fish do come. So always put it at your back.

It's clever, the internal rhymes give it a good flow, just like the river.

Did you mean shoals of fish, rather than schools? This still keeps the alliteration going.

no

Umm, what are schools of fish doing in a river?