A lake is a large waterbody, usually of freshwater, larger and deeper that a pond. Only its margins and shallow areas less than 2.5 m deep are regarded as wetlands by specialists, strictly speaking, although many inventories and the Ramsar Convention list of internationally important wetlands include whole, much deeper lakes.
Natural Lakes
Most freshwater Lakes are found inland. But some can also form near the coastline, through freshening of an ancient brackish waterbody after it is cut off from the sea, whilst still fed by freshwater streams (e.g. in the Nile or Po deltas).
In north Africa, Turkey and Spain, under dry conditions, some endoreic lakes (from which water cannot escape, except through infiltration or evaporation) sometimes form. They are fed by water run-off from their catchment. This run-off gradually brings large amount of mineral salts that accumulate over thousands of years, turning them into brackish or salt lakes (e.g. Tuz Gölü or Great Salt Lake in Turkey).
Dam lake or Reservoir
A reservoir is a man-made structure aiming at retaining and storing part of the flow of a river, stream or runoff water. They may be created by large dams or by smaller reservoir structures. These reservoirs have a number of potential uses: storing drinking water, providing water for cattle, regulating river flows downstream, hydro-electricity production, leisure activities, irrigation, water transfer to other areas, etc. In the case of irrigation, these artificial lakes can contribute secondarily to the creation of other artificial wetlands, e.g. ricefields or smaller water impoundments.
In contrast to natural lakes, the high fluctuations in water level often make these areas of little interest for fauna and flora: they are often very poor wetlands, biologically speaking.
However exceptions do exist, especially among the smaller or more ancient reservoirs. For instance, the little flood-storage reservoir at Valle Santa near Ravenna near the Po delta helped save some of the last remaining marshes in the Po floodplain, including reedbeds, Nymphea floating beds and varied fish communities. This site now features on the Ramsar Convention list.
