Lake Formation...

Lakes are formed from many different processes. Some common forms of lakes include:

Tectonic shifts: The movement of the Earth's crust can form lakes. Some of the oldest lakes on Earth are tectonic lakes. These lakes also tend to be very deep. Famous examples include Lake Baikal in Asia and Lake Tanganyika in Africa. 

Natural damming: Many natural processes can form lakes by damming a river or stream. These include landslides, lava flows, glacial debris and even beaver dams. 

A brief demonstration of lake formation by the ECHO Leahy Center for Lake Champlain.

Volcanos: Craters caused by volcanic activity can fill with water creating a lake. Volcanic lakes are often round in shape and occur near volcanos. A famous example is Crater Lake in Oregon. 

Dissolution: Water can dissolve porous substrates forming lakes. Sinkholes are an example of this phenomenon.

Rivers: Lakes can be formed when the course of rivers shift, isolating a previously connected meander. Riverine floods can also form scours that become lakes. 

Glacial retreats: Many lakes in the Northern Hemisphere were formed by glaciers. Retreating glaciers can scour the landscape, leave piles of debris, and provide melt-water, all of which can help form lakes. Some famous examples of glacial lakes include Loch Ness, the North American Great Lakes, and...Lake Lacawac!

Lake Lacawac was formed when glaciers retreated from the Pocono Mountain region approximately 13,000 years ago. The retreating glaciers created a crater in the sandstone that became Lake Lacawac. Over the past 13,000 years, the lake has shrunk to roughly 60% of its original size and has accumulated roughly 35 feet of sediment!