Dover, Strait of, is a narrow channel that connects the English Channel and the North Sea and separates England and France at their closest points. The shallow strait is about 21 miles (34 kilometers) wide and has an average depth of less than 100 feet (30 meters). Chalk cliffs rise high on either side of the strait. The ports of Dover, England, and Calais, France, are opposite each other on the Strait of Dover. The United Kingdom and France began building a railroad tunnel under the strait in 1987. The tunnel opened in 1994. Many athletes have set records by swimming across the English Channel, usually from Calais to Dover (see English Channel).
