A lake is a large body of water surrounded by land. Unlike rivers and streams that flow continuously, lakes stay in one place, fed by rainfall, underground springs, or rivers that flow into them. Some lakes are small enough to walk around in an hour, while others are so vast they look like oceans. Lake Superior, one of the Great Lakes between the United States and Canada, is larger than the entire country of Austria.

Lakes form in different ways. Some fill depressions carved by ancient glaciers thousands of years ago. Others form in volcanic craters or where rivers naturally widen. The Great Salt Lake in Utah is actually the remnant of a much larger prehistoric lake that existed when the climate was wetter.

Most lakes contain fresh water, but some are salty. The Dead Sea, despite its name, is actually a salt lake so dense with minerals that swimmers float effortlessly on its surface. Lakes support fish, birds, insects, and plants, creating ecosystems distinct from rivers or oceans. People have built cities beside lakes for thousands of years, drawn by the reliable water supply and transportation routes they provide.