I don’t need a skimmer. There are no trees or leaves where the pond is positioned.
The biggest reason to have a skimmer on a pond is to collect not only leaves but also any other debris on the surface of the water. In addition to a skimmer you will also have at least one bottom drain. These two components are your suction lines to your pump. If your bottom drain clogs for any reason, then your skimmer will be the primary suction allowing your pond to still circulate water without your pump losing prime.
Note: Even if you plan to build your pond inside your house, you should still install a skimmer because it will skim off the dissolved organic compounds (DOC). DOC will form in any pond and, if not removed, will cause bubbles and an unsightly film on the surface of the pond. A skimmer removes this film by constantly skimming it off the surface of the pond.
A skimmer can make the difference between enjoying a pond and beginning to resent it. A properly functioning skimmer will collect the leaves and anything else that lands on the surface of your pond into a net or basket, where it can be easily disposed of. Without a skimmer, you are sentenced to a life of constantly netting leaves and debris from your pond by hand. Skimmers are a real bargain when you consider how useful they are to your pond with minimal expense.
Typically you want your skimmer in an easily accessible location so you are able to dump the contents of the leaf basket and sometimes rinse it out with a hose. A good place to put a skimmer is the opposite side of a waterfall or sheer descent so the water can flow toward the skimmer to collect leaves and debris.
1 skimmer is recommended per 10,000 gallons of water.