A canal is a man-made watercourse constructed for navigation, drainage, or irrigation. Navigational canals either connect two similar bodies of water—the many canals of the Soo Locks connect Lakes Superior and Huron, for instance—or two very different waterways—the Erie Canal connects the Hudson River to the Great Lakes, employing, as most canals do, an ingenious system of locks to contend with differences in altitude. The rowdy life of nineteenth-century canalers who towed weighty barges with mule teams onshore was immortalized in the folk song “The Erie Canal,” which boasts the line, “Oh the E-ri-e’s a-rising and the whiskey’s gettin’ low.” Canals also bridge unnavigable stretches of rivers such as the Mississippi and Ohio, and connect oceans with seaports that are not directly on the coast. Then there is the Panama Canal, which links the Atlantic and Pacific Oceans.

Donna Seaman