Water lily (Nymphaea sp.).
Water lilies are considered by many to be the jewels of the pond. Not only are they beautiful to look at, but they also serve an important purpose in the pond, mainly in aiding its ecosystem. Water lilies require a lot of sun to grow properly. The flower colors are just as varied, ranging from yellow, pink, red, white, purple, blue and orange. Several types of lilies are incredibly fragrant, as well. More information about water lily at the Water Lily page.
If you want more information about this flower, just search the plant's Latin (botanical) name on Google: