Almost too easy, just point and shoot. Classic lake (or in this case reservoir) and mountain composition. Lovely clouds and reflections, dark sky overhead, light on the distant hillsides and a slight ripple on the water for texture. Even a marker buoy for a spot of colour.
I'm sure had I not been with company I might have spent longer experimenting with different perspectives, maybe a panorama, or waiting for just the right cloud formation, but I doubt the outcome would be all that different. It's a great reminder of a lovely afternoon in a beautiful place and I hope to be able to repeat the experience.