This type of picture is called "trampantojo",  a Spanish name, which means "deception" or "optical illusion". It's the technical term for an artwork that exists since the Ancient World. A work of art is being designed in a way that it imitates reality and leaves the beholder in a state between being amazed, doubting if, up to believing that something artificial is real. A trampantojo plays with the imagination of the beholder offering a surrealistic landscape to dive into...

To make the deception as perfect as possible the reflection of the trees should be crystal clear (which is a challenge with the omnipresent wind rippling the water) and something surprising, something totally unexpected should appear in the "sky". 

To achieve a "realistic" look the pictures have been turned upside down by 180 degrees.