You have used f16 aperture, 1/3000 shutter speed at ISO 800.

did you click from a boat?

Assuming that you were handholding, still you could have used a lower shutter speed. Two stops reduction of shutter speed would have given you 1/750, sufficient for handholding. So you could have safely reduced the ISO by two stops to ISO 200 for the given aperture.

For correcting the horizon tilt using Lightroom software, you can check this tutorial.
http://www.indiawilds.com/forums/showthread.php?t=1510

Cheers,
Sabyasachi
PS: One needs to login to view the tutorial. Registration is free