This single group of plants has more to do with the following than any other pond plant:
- The overall visual impact of your garden
- The chemistry of a healthy clear water environment
- The general health and well being of the animals living in the water
Visually I think that the sight of a healthy, mature, flowering water lily plant in full summer growth has very little to equal it, though I may be biased.
Chemically, any pond requires the removal of a lot of surplus nitrate which comes from fish waste, etc. This, a healthy water lily will do in abundance, purifying the water which in turn helps control the unsightly green water algae.
Fish have, as an added bonus, the security of the shade produced by the lily pads, thus reducing their stress and improving their general health. Furthermore by blocking the summer sun you reduce the visibility for predators like herons.