Which aquatic plant is in the picture?

Nymphaea is a genus of hardy and tender aquatic plants in the family Nymphaeaceae. The genus has a cosmopolitan distribution. Many species are cultivated as ornamental plants, and many cultivars have been bred. Some taxa occur as introduced species where they are not native, and some are weeds. Plants of the genus are known commonly as water lilies, or waterlilies in the United Kingdom. The genus name is from the Greek νυμφαία, nymphaia and the Latin nymphaea, which mean "water lily" and were inspired by the nymphs of Greek and Latin mythology.

Water lilies are aquatic rhizomatous herbaceous perennials, sometimes with stolons, as well. The stem is angular and erect. The leaves grow from the rhizome on long petioles(stalk that attaches the leaf blade to the stem). Floating round leaves of waterlily grow up to 12 inches across. The disc shaped leaves are notched and split to the stem in a V-shape at the centre, and are often purple underneath.