The network of Polish waterways, comprising navigable canals and canalised or free-flowing rivers, as well as a number of interconnected lakes, is nearly 3650km long. Waterways of international importance (classes IV and Va) represent only 1.9 and 3.0% of this length respectively. The main waterways are the Oder, the Vistula and the Vistula-Oder waterway. The Vistula-Oder waterway is most important waterways for tourism in future.