The first two have the main focal point of the image right down the middle of the frame, try ofseting it to either side (rule of thirds). Otherwise the image looks way to symetrical and "staged" (for lack of a better term).
The last one is a great shot, i love the sky and the water (looks HDR to me) but maybe i'm wrong. Try rotating the image so your horizon is flat throughout the frame...right side looks higher. Also a crop from either the top or bottom would make it more pleasing to the eye (same as above...rule of thirds) the horizon cuts right through the center of the frame. Crop whichever you don't want to be your main focal point...the water or the sky.
But otherwise good work, keep shooting!