Technical data: Canon EOS 70D + Canon EF 100–400 mm f/4–5.6 L IS, ISO 320, 400 mm, 1/500 sec, f/10.
Is this issue caused by air turbulences over the water? Thank you.
This distortion is due to the sun shining on the water. The sun's heat warms the surface causing warm air to rise. Likely some water vapor mixed in. What happens is, different layers of different density air alters the path of the light rays from the principle subject. There is little you can do to mitigate. A UV filter or polarizing filter might provide a smidgen of help but this is something we live with.