A cofferdam is a temporary structure used to create a dry work environment in areas that are usually submerged in water. It is typically made of steel, concrete, or earth and is constructed around a specific site, allowing workers to perform tasks such as construction or repairs without interference from water. Cofferdams are commonly used in projects involving bridges, dams, and marine construction. They help to control water levels and protect the work area from flooding, making it easier to install foundations or conduct maintenance on existing structures.