Impoundments - Lentic Ecosystems
We have so far discussed natural lakes. In addition to these there are a number of lakes both small and large artificially created by man called reservoirs or impoundments. These have been built to fulfil specific requirements - hydroelectric power generation, fisheries, water supply, irrigation, industries, recreation, control of floods, etc.
Impoundments may be called Offstem or Onstem depending on how they have been created. Onstem reservoirs - these are located in upland areas and are formed by damming a stretch of river or stream in a suitable river valley. In India only these types of impoundments are found. Offstem reservoirs are built in low land areas by pumping water some distance from a river or from an underground source.