Possible cause #1 Heat distortion. Try take multiple shots/clicks so you will have higher keepers.
@MikeInPA just mentioned it above. Not much processing can be done if image were caused by heat distortion.
Possible cause #2 Shiny reflective furr. Happens to me often esp when shooting blue-throated bee-eater. Try again when no direct light shine on the subject or in overcast condition or in shadow.
Possible cause #3 Shutter speed. The subject may appear not moving much but the water is. Again, same as above, take multiple shots to allow you to get higher keeper even at 1/500s. Maybe within 10 shots, 1 will get sharper when the exact "click" moment were in perfect condition. For me, if subject is far away and small, I will start shooting at at least 1/640s or 1/800s incase some strong breeze.
Possible cause #4 Too shallow DOF (low aperture). If in auto, my best practice is go with shutter priority but that will leave aperture and ISO in auto. From your shot, the aperture is at F4 which quite shallow. If you can, try shoot manual, leave ISO in auto. My best ideal aperture is F9 for all my general handheld shooting using full frame A7Riii + Sony FE 200600, 1/640s (may go down to 1/320s if subject not moving much). This you will need practice, trail and error see which best aperture is ideal for your shooting style.
Remember the longer reach you zoom out, the more steady hand is needed. I shoot AF-S (spot), I don't think shooting AF-C will be an issue if the auto focus able to keep up. In your case, not much object distraction around the subject.
Happy shooting.