Lakes and Ground Water

                 Natural lake occurs where a large quantity of water collect in a hollow  in impermeable rock, or is prevented from draining away by a barrier, such as moraine or solidified lava. Lakes are often relatively short-lived landscape features, as they tend to become silted up by sediment from the streams and rivers that feed them. Some of the more long lasting lakes are found in deep rift valleys formed by vertical movements of the earth crust. For example, lake Baikal world's largest fresh water lake and the dead sea in the middle East, one of the world's saltiest lake. Where water is able to drain away, it sinks into the ground until it reaches a layer of impermeable rock, then accumulates in the permeable rock above it. This water saturated permeable rock is called an aquifer. The saturated zone varies in depth according to seasonal and climatic changes.