This pretty plant may look like a water-lily, it even has the words water lily in its name but it’s not actually a member of the water-lily family.
This is the Fringed Water-lily (Nymphoides peltata) and its closest plant relation is the Bogbean (the fringed edges to its petals are a bit of a giveaway). It can be found in ponds (the one in my photo is in the dipping pond at Cosmeston Lakes Country Park), lakes and other watery places where the water is still or slow moving. Apparently, it is well established in the Leeds and Liverpool canal, and in much of south-east England, as well as in the East Anglian fens. It is also widely planted in ornamental ponds in parks and gardens, and snippets of those plants may account for its spread in the wild. The gardeners amongst you may know it as Yellow floating heart, which is such a charming name, I think.