A pond pump is attached to the electrical supply and submerged at the bottom (there are external pumps as well) of the pond. It delivers all the power to circulate the water through waterfalls, fountains, ornaments or just backyard ponds.
An effective pump and circulation system is necessary for the ecosystem of your pond. Pumps that circulate water in ponds and other water features keep the water moving, supplying the required oxygen levels for healthy fish and plants and upsetting insect aggregation.
A good rule of thumb for assessing how large pond pumps should be to provide just filtering is to select a pump that will turn half the water volume around of the pond per hour. So, if you have a pond with 1000 gallon volume, a pump that will pump 500 gallons per hour is sufficient.