Last week you asked me if I use ND-filters.
Well, this summer I did some practice with a ND-filter. I used it by a waterfall and I can say that it is a usefull filter. Often on places with moving water you want to use slow shutter speeds. Normally, during the day you cannot reach 1/15 sec. often not even with f/22. The ND-filter is helping you to give the right blur-effect to the water. Here in your fossen picture I see your exposure figures are f/7.1 with 1/640 sec.
Here it was possible for you to use f/22 to get a slower shutter-speed.(tripod). By doing that you might get more movement in the water. When that still gives not enough effect, than the ND-filter is an option to use. But it is a matter of what you like best.
Peaceful Rest (37) *