I recently sold my pro camera and lens and downgraded to an Olympus mirrorless. A used lens I bought, the Olympus M.Zuiko Digital 12-50mm, I have been doing long exposure shots with. Here is an example photo I took. Do you see the black smudgey area above the bottom rocks? These are not caused during editing, this is unedited. They are captured during the long exposure. What are they called?? Is my lens broken or is this fixable? My pro setup never had this problem. It is there in most of the long exposures I have taken. So I have added a second photo. See the black streaks on the water above the black rocks in the middle of the picture? After further investigating, I realise these are only in the long exposure pictures I am taking when I use an ND filter. SO, that would mean these are being caused from the filter. What does that mean? Crappy filters??
Not a problem with your equipment. They are reflections of the clouds. Non-smooth water will cause vertical smears. The effect is subtle here, but it is more obvious when the sun is reflected.
Edit: More evidence, an example of vertical smearing from my library:
Also note that the clouds in the sky in the OP's pictures are not blurred, so the exposure was not very long. It is not caused by a long exposure.