Even a small pond the size of a washing up bowl can be useful for wildlife. The important thing is to have some plants that allow animals to hide and also the herbivores to eat. A shallow edge which allows animals to climb in and out is also valuable. If you have your pond in a tub make sure you put some sort of step in it for the same purpose.
A stone can be a useful place for a frog or other creature to hide in your pond and a mix of plants that float on the surface and emerge from the water is ideal. Frogs are wonderful animals to encourage into your garden because they may eat pests such as slugs for you. As they can spend very little of the year in water make sure then that you have some vegetation where they can hide and some stones or logs where they can overwinter.
