(I wish you would have posted a larger image.)
You've got a good start. You're going to need to add bits of lighter blues and white to indicate the crests where the sun is glancing off, and darker blues and washes of indigo to indicate the shadows of the troughs between the swells. You've already got a start at this, and, tedious as it might be, you have to continue. Something's missing, though. Can you see it?
You've got a
ightening down at the far horizon, but your shadow beneath the dock indicates that the sun is early afternoon or late morning. By the shadow's lay, you should
ighten your sky near the top of the canvas in exact correlation to your shadows.
Next, were it mine, I'd mute the colors of the lake just a bit. Though water is this blue in some lakes and rivers in the West where I live, on Lake Pend Oreille where I live, it's a grayer muted blue. Water will take on the hues sky, its surroundings, with toning by algae and minerals like copper...or pollution.
These will produce everything from muddy coloros, to orange and pinks waters. The presence of copper creates a startling torquoise
ightness, especially in the depths, prevalent in the West.