Six seconds is long enough to smooth the chop and short enough to keep the shape of the break. The window is narrower than you would think — at three the water is still busy, at fifteen it is fog.
Shooting into the sun means the filter does two jobs: it buys the shutter speed and it keeps the highlights from tearing. A cheap one will give you a magenta cast across the whole frame that no amount of white balance will fully undo.
This was the last frame before the tripod started sinking.