This effect was generated in Filter Forge, a Photoshop plugin that allows you to create your own filters.
This is a filter for altering the sky in landscape pictures, particularly for making sunsets within that sky. It relies on a variance between luminosity of the ground and the sky and will divide those areas within the filter and then alter mostly just the sky, with a smaller effect to bathe the land with the sky effect.
If adjusted correctly, it should also show the sky effect on water as a reflection.
Craig Kraellin Walters sky sunset lumiosity threshhold horizon skyline reflection water