Pond lily or water lily are also known as Nymphaea. They are the most well known pond plant mainly because of how large the lily pads can grow. And how many wonderful colours the flowers can come in.

The flowers really however only flower in the summer, but the lily pads can keep going. They can be very helpful to have, as the can provide shelter for fish, to hide out of sight from herons, and also shade for the fish from the sun.
Lily plants can grow over 8 meters and spread beautifully around the pond.
There is a dwarf species of lily these can grow up to 60 cm. So these are good to have in smaller ponds.