A giant man named Paul Bunyan hiked across New York State. His heavy footfalls shook the forests: boom, boom . . . and then he tripped. As he tumbled toward the ground, Paul’s hand broke his fall. Long, narrow lakes appeared in the earth where his fingers had been.

At least, so goes the tall tale—the very tall tale—about the creation of New York’s famous Finger Lakes. This myth is a fun part of America’s folk history. But where do lakes really come from? During the ice age, glaciers moved slowly along Earth’s surface. As they moved, they dug out pits. When the glaciers melted, water filled those pits. Voila! Lakes everywhere! Lakes can also form when parts of the Earth’s crust break and leave holes. Rain or nearby streams fill those holes with water. The holes of empty volcanos can fill with water too, making lakes.

Some lakes are created when a barrier stops a body of water from flowing. During a mudslide, mud, rocks, and other earthy materials hurtle down a hill. If enough of that material falls into a stream, the stream will be blocked from flowing. It will become a lake. Beavers can also make lakes by blocking the flow of streams with dams.

Sometimes, people make lakes too—and not by falling down like Paul Bunyan. They use machinery to dig huge holes they fill with water. They also block existing streams. These manmade lakes can be used for things like irrigating crops, fishing, and generating electrical power.