A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Ponds can be created by a wide variety of natural process (e.g. on floodplains as cut off river channels, by glacial processes, by peatland formation, in coastal dune systems, by beavers) or they can simply be isolated depressions (such as a kettle hole, vernal pool, prairie pothole or simply natural undulations in undrained land) filled by runoff, groundwater, or precipitation, or all three of these. Ponds may be freshwater or brackish in nature. 'Ponds' with saltwater, with a direct connection to the sea that maintains full salinity, would normally be regarded as part of the marine environment because they would not support fresh or brackish water organisms, so not really within the realm of freshwater science.
Ponds are usually by definition quite shallow waterbodies with varying abundances of aquatic plants and animals. Depth, seasonal water level variations, nutrients fluxes, amount of light reaching the ponds, the shape, the presence of visiting large mammals, the composition of any fish communities and salinity can all affect the types of plant and animals communities present.Ponds are frequently man-made or expanded beyond their original depths and bounds by anthropogenic causes. Apart from their role as highly biodiverse, fundamentally natural, freshwater ecosystems ponds have had, and still have, many uses, including providing water for agriculture, livestock and communities, aiding in habitat restoration, serving as breeding grounds for local and migrating species, decorative components of landscape architecture, flood control basins, general urbanization, interception basins for pollutants and sources and sinks of greenhouse gases.