Steamboats played a major role in the 19th-century development of the Mississippi River and its tributaries, allowing practical large-scale transport of passengers and freight both up- and down-river. Using steam power, riverboats were developed during that time which could navigate in shallow waters as well as upriver against strong currents. After the development of railroads, passenger traffic gradually switched to this faster form of transportation, but steamboats continued to serve Mississippi River commerce into the early 20th century. A small number of steamboats are still used for tourist excursions in the 21st century.