It’s fun to take pictures of water in the summertime! 🙂
To get that soft, foamy effect, use the slowest shutter speed possible (at least a couple of seconds). To do this, you may need to wait until dark (or be in a shadowy forest, or have a neutral density filter on your lens). Stop down your aperture as much as you can … I think I used f/22. Also, I didn’t have a tripod, so I perched my camera on a rock and used the built-in timer instead of my remote.
It’s important to have something perfectly still in the shot, to give it an anchor, so to speak. Rocks are good for this purpose!