What is a Lake?

A lake is an enclosed basin filled or partly filled with water, typically it is relatively deep and large enough to produce a wave-swept shore.

A lake may have a stream inlet and/or an outlet, or it may be completely enclosed (landlocked).


Many lakes in Illinois are man-made impoundments of rivers. Carlyle Lake is the largest man-made lake in Illinois, formed by building a dam across the Kaskaskia River in 1958.


Other lakes were formed as the glaciers moved across Illinois during the ice ages. Lake Defiance was created from a chunk of ice that broke off of the receding glaciers 15,000 years ago.


The largest lake in Illinois is Lake Michigan, part of the Great Lakes. 

The Great Lakes are the largest surface freshwater system on Earth, containing approximately 20% of the world's surface fresh water. 

The Great Lakes were were formed by the glaciers during the ice ages.