A dam is a structure built across a stream, river or estuary to retain water.
Some dams are tall and thin, while others are short and thick.
Dams are made from a variety of materials such as rock, steel and wood. We will concentrate on dams made from concrete, a complex material, because it is important for the construction of large dams. Well, dams are really the product of many people, but civil engineers are usually key players. Keep your eye out for this cee symbol to point out things that civil engineers do. An obvious example of a societal structure is a bridge.