This is a very Florida Keys looking shot. I've seen it almost this red down there a little after sunset. This would be shot from somewhere at or near Marathon from your MM info. The vignette is a natural thing there too, when shooting sunsets with a very wide lens, because the light actually does off pretty fast going away from the sun around the horizon. I do agree thought that it would look more natural and pleasing a little less saturated and not as purple with the tint.
In response to your request for comment, I feel that you've relied almost entirely on colour for this image, and the colour choice you made is not a good one.
I can make nothing of the scene from what's presented here, and so I have no feeling for it. I feel overwhelmed by what must surely be an artificial colour cast. Your decision on vignette, in my view, is misguided: you are visually clamping down on a subject matter that wants to be an open vista. Unless you have a very good reason for doing so, vignetting a vista should be avoided. The result here is slightly disorienting and subtly cramped.
I'm not a member so I can't vote on member challenges. Instead, I look through the entries for images that make me stop clicking on to the next one. This is one of those images....
Now that's intense. I'm generally not a big fan of such deep saturation, but I can't help liking this a lot. Makes me wonder what the original really looked like. Then again... makes me not really care. Nice effect. Hope it does well.
I like it, colors are stunnig, composition is perfect, in my fav's.. is a very difficult challenge, but I wish you could finish in a good position ... 8