The Oise is a river of northern France, approximately 480 km in length. It is a tributary of the Seine and flows through the Picardy region. The Somme is another river of northern France, approximately 300 km in length. It is a tributary of the English Channel and flows through the Picardy and Hauts-de-France regions. The Yser is a smaller river of northern France, approximately 80 km in length. It is a tributary of the North Sea and flows through the Nord-Pas-de-Calais region. All three rivers are important to the region and provide a variety of benefits to the local population.