Where seaports are located inland, they are approached through a waterway that could be termed "inland" but in practice is generally referred to as a "maritime waterway" (examples Seine Maritime, Loire Maritime, Seeschiffahrtsstraße Elbe). The term "inland waterway" refers to navigable rivers and canals designed to be used by inland waterway craft only, implicitly of much smaller dimensions than seagoing ships.
In order for a waterway to be navigable, it must meet several criteria:
The European Conference of Ministers of Transport established in 1953 a classification of waterways that was later expanded to take into account the development of push-towing. Europe is a continent with a great variety of waterway characteristics, which makes this classification valuable to appreciate the different classes of waterway. There is also a remarkable variety of waterway characteristics in many countries of Asia, but there has not been any equivalent international drive for uniformity. This classification is provided by the UN Economic Commission for Europe, Inland Transport Committee, Working Party on Inland Water Transport. A low resolution version of that map is shown here.
Media related to Waterways at Wikimedia Commons