I endorse the comments and crops posted by nartreb and Dave Metsky.
Centering the primary visual feature (the mountain peak) left-to-right in this scene is of far more concern to me than placement of the horizon. The symmetry of the reflection almost begs to have the horizon more-or-less centered. So:
1) Crop horizontally to eliminate the white wedges in the upper right and lower left of the frame. When this is done, you have the real image with which you can work.
2) Don’t mess much with further horizontal cropping. Instead, play with vertical crops that move the mountain peak to various left-right positions in the frame.
Remember, the rule of thirds should be used as a point of departure – a starting point – for composition, but only that. It provides excellent guidance in many or most cases, but is not inviolable.
Nice shot, by the way!
G.