I love the shot and the effort to create a beach but not sure after all the effort to create a cool beach that leaving the bottle was helpful, I personally like every part of the image other than the bottle. The focus and exposure on the frog are dead on and your mini beach, water and sky look almost natural. Nicely done, I will give it a 7 but think I would have gone 1 or 2 points higher without the bottle.
Considering that this challenge was, in its description, expanded to include waterways and lakes etc, I have a hard time judging this beyond a shoehorn. At best, it's an attempt to make a stock shot where one was not needed in the least, and it is somewhat awkward in this respect, with the bottle of sand floating upon the "water." Things are believably set up if one were to ignore the scene, sure, but for such technical quality seen in the bullfrog, I'd wish this were produced in a natural setting, where the suspension of disbelief was complete and not so fabricated.
Well, it's a frog, so my first thought is Lydia :-) Whoever you are, nice attention to detail with the cloud/ocean bg. And the giant container of sand floating on it :-)