The use of rivers as transport corridors offers a cost-effective and environmentally sustainable alternative to road transport, facilitating the seamless movement of cargo from major maritime hubs to hinterland port cities. The objective of this research is to design an efficient transport service, inspired by the principles of the Physical Internet (PI), in a network that includes seaports and a set of river ports. This specific network is a missing link between local/regional road networks and deep-sea transportation lines. We consider the location of PI hubs as well as the determination of transportation routes, vessels and frequencies. We propose a mixed integer linear programming formulation of a service network design problem in the river network and explore the impact of a few business constraints inspired by the rules of the PI.