Oxygen is essential for life.  It forms the backbone of water.  It's the most crucial element for vertebrates; we need it constantly.  Just a few minutes is the maximum time we can be without it; no other element is as vital to supporting life as we know it.    

As vertebrates, fish have these same needs for oxygen.  Only instead of breathing it in from the air, they extract it from the water with their gills.  This oxygen they are extracting isn't being torn from the water molecules themselves.  They aren't pulling the the O from the H2O.  The oxygen they absorb is 'dissolved oxygen', stable O2 molecules that become dissolved into the water through aeration and agitation,  the same O2 that we breathe from the air.  ​

Environmental Conservation
Sustainability has become a big focus in the modern world, and water plays a crucial role as the world's greatest resource. An Ecosystem Pond is self-sustaining, requiring little maintenance. Initially filling the the pond will require a good bit of water, but over the long haul it uses less water than the area of lawn it replaced.  A healthy Ecosystem Pond will attract all kinds of wildlife: frogs, salamanders, turtles, birds, butterflies, dragonflies, snails, even thirsty mammals may stop by your pond for a drink.  Certified wildlife habitats are growing in popularity, and water is one of the elements required to achieve certification. Water gardening becomes your new hobby as you feel yourself drawn to its beauty and natural elements.
A pond provides opportunity to have fish as pets, without the mess and maintenance of an aquarium. Aquatic plants give you the chance to broaden your gardening horizons with choices that go beyond the standard petunia and rose. In addition, bird lovers will delight in the new variety of feathered friends that flock to a water feature. Nature lovers simply can't go wrong with water features.