I had two cameras with me for this image, a Minolta Autocord circa 1955 and my fairly new Fujifilm; I guess I was hedging my bets! I continued working with both cameras as the light faded, gradually lengthening the exposure to completely smooth the water. I didn't have an ND filter for the Fujifilm; of course, there isn't one for the Minolta.
I enjoy the process of long exposure immensely. There is a meditative element involved as the camera quietly gets on with its job, and the photographer has nothing to do but stand and watch the fading light.