Right now it seems very flat -- dont be afraid to overdo highlights and shadows because you can always pull them back. Your background and the water are solid colors; try working some sort of, well, background into the background such as clouds, sky, landscape, ect. and try getting some shadows and highlights into the water. Water can be a very hard subject to give liveliness to, even for the experienced, so I highly recommend finding some good reference photos via google images.
Overall, good solid start so far; just keep retouching and refining, and you're good to go!
