If you are fortunate enough to have the space and the time to establish a small pond in your garden, take the time to learn about the plants that are most suitable for your purposes and the climate they’ll be growing in.
Oxygenating plants are a good choice, as they help keep the water clear of algae and provide cover for fish and other wildlife. Most grow underwater and do not root in the bottom, so it’s easy to control their growth. A couple of the best options are hornwort and curly pondweed, both hardy native plants that can survive a British winter, and the curly pondweed even blooms with delicate pink and white flowers in early summer.
Water violets are also oxygenators, and though they’re a bit harder to get started, it’s worth the effort. Besides producing lovely flowers that grow up to ten inches above the surface, they can thrive in water up to two feet deep. Water lilies, on the other hand, are an established favourite but not always the best choice for a small pond, as they require a lot of light. Others that do well in deeper water and can handle shadier conditions are Brandy Bottle (common pond lily) and Golden Club.
Floating plants like water hyacinths and fairy moss are notoriously invasive, but in small garden ponds they are easily controlled and add a lot of character. Marginal plants that grow in the very shallow water along the edge of a pond can be wonderfully decorative. Yellow Flag and Harlequin Blue Flag Iris, Marsh Marigold and many others are all good options, but note that most of them tend to be invasive so you have to watch them closely or they can take over the pond.