White-water rapids is my guess, but the original website is a 404 error page, and so far the pinners I've checked haven't listed what it is, except snow. The motion doesn't seem to correlate with snow.
This piece works with shadow art, which I find very interesting. I love pieces with crisp lines and the affect of the nails has exactly that. The contrast between the white wall, dark nails, and light shadows is dramatic, yet simple.