Even if you haven't created a pond specifically to attract wildlife, it will come.  Some animals like deer and most birds will just drop by for a visit.  In the spring, you may find that the sound of a waterfall or a fountain will attract birds you have never before seen. Other creatures may also take up permanent residence near your pond.  My pond has many frogs and I never purchased any of them!

Consider adding scavengers to your pond.   Enough cannot be said in favor of scavengers for your koi pond.  These scavengers clean up algae and spent vegetation in the pond.  They are the houskeeper of the pool and water garden.  Your fish feed upon insects; snails devour algae and green scum; tadpoles eat decayed matter, and clams or mussels continuosuly filter the water to keep it clear.  While toads will eventually hop away to live on land,  frogs will remain in and close to the Koi fish pond.  Frogs do remain in and near the pond.  Their diet consists mainly of insects, although bullfrogs (they can grow to six inches long) are capable of eating good-size fish.  Toads will keep bugs and slugs away from your garden.  Frogs live off of insects.   Both toads and frogs may decide to inhabit your pond naturally.  As a matter-of-fact, most wildlife experts advise against buying bullfrog tadpoles which have voracious appetites, but instead waiting for smaller, sometimes endangered, native frogs to colonize your pond.  

Clams or mussels also make good scavengers for your Koi  fish pond.  They act as natural filters.  You will need to provide them with a shallow bed of sand for them to burrow into.  You can buy them now at Live Aquaria.com!  Beware, though, if you have Koi, your fish may eat them.

When designing my Koi pond,  I added a waterfall with a pond area for it to dump into, connected to a stream that leads into the main pond where I keep my Koi.  These koi pond scavengers need to be kept separate from the main pond if you have large Koi fish.  I keep the mussels and clams in the waterfall pond and the stream.  It is very difficult to keep mussels with the Koi pond fish as the Koi, especially the larger Koi Carp,  think of them as food.  Your Koi will work in pairs to get at the mussels, with one Koi squirting the clam so it opens its shell, while the other Koi fish attacks. 

Snails are often offered by water-garden suppliers to help keep ponds clear of algae, decaying vegetation, and wasted fish food.  A variety of snails should be selected since each has a different appetite and function.  The most commonly offered are the ramshorn snail which has a spiral shell, and the black Japanese or trapdoor snail.  Of the two, the trapdoor is preferred because it won't snack on your prized plants.  You can buy it now at Live Aquaria.com       

Newts, a cousin of the salamander, and a good scavenger to have for your Koi pond, begins life in the water as larvae, then spends two years on land, eventually returning to the Koi pond water.  These scavengers will hunt insects, crustaceans, and worms.  In the spring mating season you will notice that the males develop showy crests.  One quick note about these pond scavengers is that once the newt and salamander scavengers are added to your pond you will probably not see them.  I purchased a few for my pond, but never saw these scavengers until I moved my fish to their new home.  If you are purchasing them with the intent of watching them, you will probably be very disappointed.