Not Waving but Drowning
Not Waving but Drowning Setting
We have something of a mystery on our hands here. We know someone died, we have some guesses about how, but the location is never stated. So we have to make some guesses based on context.
If he was literally drowning, he must have been doing so in some body of water. Then, if people are standing around commenting on him, probably the scene is slightly different. Could it be on the shore after his body is pulled out? Or is it at his funeral, maybe his wake, as people gather around to remember him? What if the dead man is speaking from his grave or the afterlife? We just don't know.
The timeline is a little easier to reconstruct: guy dies, dead guy complains, folks talk about him, dead guy blasts them for getting it all wrong. It's not very specific about dates or how much time passes, of course, but at least it's a clear sequence.
The one surprise comes in the final stanza when we learn that the dead man didn't struggle just the once, but instead spent his life drowning. You could say his death wasn't a single event, but a long, lonely process. The setting, then, isn't even a real seashore, but instead just the poor guy's depressed mind. Hey, no one ever said this poem was a trip to paradise.