This is a hardy waterlily cultivar. Nymphea something or other. We've had it for years and I've never pinned it down. What I can be sure of is without Joseph Bory Latour-Marliac we wouldn't have it.
By hybridising tropical colored waterlilies with hardy european species JBLM unleashed hundreds of new cultivars and changed the face of our ponds forever. Oh and he helped a certain Monsieur Monet make the view of his water garden a bit more interesting too.