Sky replacement is one of the biggest trends right now, with many programs offering replacement capabilities at varying degrees of automation. Photoshop recently added a powerful sky replacement feature, and though it does not handle water reflections automatically, it is not that difficult to add them manually, and this fantastic video tutorial will show you how it is done.
Coming to you from Blake Rudis with f64 Academy, this great video tutorial will show you how to replace a sky automatically in Photoshop and add a realistic reflection in water. The challenge with creating a water reflection is that it is almost never a perfect reflection, but rather has some blurriness due to motion in the water. Even on relatively windless days, most lakes or other bodies of water will have some amount of motion in them, and as such, you need to simulate that to achieve a level of realism. Beyond that, adding perspective correction can help to finish off the effect. Check out the video above for the full rundown from Rudis, and download his action here.
And if you need some more skies for your library, check out "Mike Kelley's Ultimate Sky Library" Royalty Free Raw Photographs for Sky Replacements With Mike Kelley!"