This was an interesting accident. The last time I had used my dSLR, it was for some low-light work with lots of motion. In order to get acceptable images, I had to crank up the ISO to 1600. Pretty high. When I was done with that shoot, I forgot to reset the ISO rating back to 200 (the lowest it will go, which is kind of a weak point on the dSLR, but so it goes.)
So when I started at the falls, I noticed the shutter speed was too fast for the available light, but only after I had snapped off a few rounds. That's when I realized what ISO I was shooting with.
As it turned out, it made some rather interesting effects, this shot being a prime example.