 Many different systems are used in limnology to number waterbodies such as lakes, rivers and streams, ranging from basic index numbers representing their location in the river system, such as serial numbers for the major catchment areas of the rivers, or numbers indicating their hierarchical position in the system.On the basis of such numbers the aim is to give waterbodies, river sections or catchment areas a clear identification number.As a result of the systems used in various specialist fields there may even be different national and regional waterbody index numbers for the same body of water.