Monet is perhaps the most famous of the Impressionists, especially for his paintings of the reflections in the lily pond at his Giverny garden. This particular painting, shows a tiny bit of cloud in the top right-hand corner, and the mottled blues of the sky as reflected in the water.
If you study photos of Monet's garden, such as this one of Monet's lily pond and this one of lily flowers, and compare them to this painting, you'll get a feeling for how Monet reduced detail in his painting, including only the essence of the seen, or the impression of the reflection, water, and lily flower. Click on the "View full size" link below the photo above for a larger version in which it's easier to get a feel for Monet's brushwork.
Palettes and Techniques of the Impressionist Masters: Claude Monet
Step-by-Step Demonstration of Painting Monet's Bridge
Photos: More Lily Paintings by Monet
The French poet Paul Claudel said: "Thanks to water, [Monet] has become the painter of what we cannot see. He addresses that invisible spiritual surface that separates light from reflection. Airy azure captive of liquid azure ... Color rises from the bottom of the water in clouds, in whirlpools." (Quotes source: p262 Art of Our Century, by Jean-Louis Ferrier and Yann Le Pichon)