All my Guadalupe River images (
www.martysphotography.com/HAAB2) were shot with my Nikon D300, Nikkor 28070 f2.8 lens (with circular polariser) ... plus ny SB-800 flash for fill and catchlights (no tripod).
On the shot of Damaris you mention, I got luck ... I slowed down my shutter to 1/25 so I could blur the water and told her to ly very still (despite the very cold rushing water that almost washed away her bikini bottoms) The only post production corrections I did to the shot was to add contrast and shift the color of the brownish water to a more pleasing blue color ... then finish it off with an unsharpen mask.