It looks like the body of water is an ocean, rather than a lake. One of the qualities of the ocean as it interacts with land is that the waves, no matter how small, are always either rolling in, or sweeping out. The water along the shore line is never in a state of rest, like you have in your image. Also David's suggestion of darkening the sand near the water line is a good one.
Having said all that, getting a convincing water/land transition is really difficult. What you have already there looks beautiful. I love the colors.