Canals are man-made waterways that are built for various purposes such as transportation, irrigation, and drainage management. They are designed to allow boats and ships to pass from one body of water to another, and can also be used to transport water for human uses. Canals can be located within a bay or open sea, can connect two or more waterbodies, or may even form networks within a city. They can be thought of as artificial waterways that carry free, calm surface flow under atmospheric pressure.

Canals can be constructed with a series of dams and locks that create reservoirs of low speed current flow, which are referred to as slack water levels. Locks are an important part of many canals, especially in areas where the land is not completely flat. A lock is a stretch of canal blocked off at each end by strong gates. These gates can be opened or closed to allow water to fill or to drain from the lock.

Builders often line the canal with stone, concrete, or steel to make it stronger and prevent water from leaking out. The oldest known canals are aqueducts built in Mesopotamia thousands of years ago, and since then, canals have played an important role in connecting cultures and facilitating commerce.

Some famous examples of canals include the Grand Canal in China, which is the worlds oldest canal still being used today and the worlds longest canal, with a length of about 1,085 miles (1,747 kilometers) . The Erie Canal in New York was an important shipping route in the 1800s, and the Suez Canal in Egypt connects the Mediterranean Sea with the Red Sea, serving as the shortest water route between Europe and the Indian Ocean.