waterway, natural or artificial navigable inland body of water, or system of interconnected bodies of water, used for transportation, may include a lake, river, canal, or any combination of these. The existence of waterways has been an important factor in the development of regions, for the waterways have served first as paths of exploration and new settlement and later as avenues of commerce and trade. Although slower than rail, road, and air transport, water shipping is less expensive and accommodates such bulk cargoes as coal, ores, grain, and lumber. Navigation on waterways may be improved by the construction of canals, dams, locks, levees, and dikes; channeling straightens and shortens water courses, and dredging deepens the channel. Waterways vary in size from shallow barge-carrying rivers and canals to the deep seaways that accommodate oceangoing vessels. Waterways are often of international importance, either because they border or run through more than one country or because other nations wish to use them for trade; a number of these waterways have been internationalized. For purposes of navigation, irrigation, and flood control, humans have changed the natural flow of waterways. The consequences of such changes have often led to excessive erosion or an increase in flooding.