There is a technique for photographing water that has become fashionable. The idea is to make moving water look smooth by setting a slow shutter speed rather than a fast speed that would freeze the motion.
To do this you need a shutter speed of at least a few seconds, usually longer. The problem is that, even at 100 ISO, with a small aperture, there is often too much light. Photographers employing this technique therefore use a neutral density filter to reduce the light entering into the camera. One of the most popular of these filters is the Lee Big Stopper which looks totally black and gives a 10 stop reduction to the amount of light passing through it.
To explain what this means:
Suppose the correct exposure of a scene at ISO 100 was 1/10th of a second at f16. With the Lee Big Stopper the exposure would become 4 seconds at f16 because each stop of reduction doubles the time needed for a correctly exposed image.
As you can imagine, for such a long exposure you need a tripod or some other rigid support.
Favourite subjects for this style of photography are the sea, streams bubbling over rocks and waterfalls. To be honest, because of its popularity, you do see many photographs that are very similar and only a few that stand out like this one.
I can imagine that this was a remote location which took some time to find. Speaking of time, the photographer had to be there when the light was coming from the right angle otherwise that water would have not been white. In this case the light is from behind and to the left which is just perfect. There has been quite a lot of post processing the digital image to get to this but the result is clearly worth it.