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.