A pond expert once explained to me that, once a pond has been created, it is dying in the sense that the water plants tend to grow at such a rate that they gradually become a solid mass, turning the pond back to dry land. To keep the pond viable, from time to time the plants, especially non-native oxygenators like Canadian waterweed, need to be drastically thinned out.
With four garden ponds (My wife has a theory that I would really like a moat and has vetoed the creation of a fifth in the front lawn) this is no small task and I do not thin them all out each year. This is partly due to the work involved but also because, beneath the placid water surface of each one, lies an aquatic jungle full of small creatures grazing, browsing and predating one another. Removing the plants often removes many small animals with it so is best performed in autumn when most of the frogs and newts will have left to look for hibernation sites beneath stones or logs or piles of leaf litter.
Leaving the plants beside the pond for several days is said to allow the animals to return to the water. However, I doubt the ability of many to do so and spend as much time searching through the piles of removed debris as I do in getting it out in the first place. I then return to the water the assortment of water snails, tiny damselfly and much larger dragonfly nymphs as well as an occasional very small, almost translucent palmate newt, no longer a tadpole and fully developed but perhaps too tiny to yet survive on land.
By far the most impressive of these creatures are the dragonfly nymphs or larvae, between one and two inches of fearsome looking predator like armoured, non-flying versions of the dragonflies, right down to embryo wings, into which they will eventually metamorphose. Most of those in our ponds are the nymphs of southern hawkers (pictured) which emerge as adult dragonflies from late June onwards after spending at least two winters beneath the water.
Dragonflies are primitive insects and develop from egg to larva to adult without going through the pupa or chrysalis stage of later evolving insects like butterflies and moths. Their prehistoric appearance is no coincidence for their history goes back to the time of the dinosaurs and long predates our own.