The main aim of this article is to present a method to process Inland AIS (automatic identification system) data that is part of RIS (river information services), as well as to synthesize and visualize information obtained from it for further analysis. This article presents problems with imaging the position of inland navigation units in the immediate vicinity of the Długi and Kolejowy Bridges in Szczecin. The passing of 80 inland units on this section of the Western Oder River was analyzed. Data were obtained from the AIS message database and industrial cameras of the RIS Monitoring Centre at the Inland Navigation Office in Szczecin. 35 units were equipped with AIS messaging devices. This article analyzed the data after previous processing, which consisted of selecting appropriate research units and decoding AIS messages recorded in the VDM message type (VHF Data Link Message). Then, the acquired positions of inland navigation units on the map were visualized to calculate the number of errors and their location. The obtained data were used to illustrate the locations of interference during the operation of transmitter-receiver equipment that prevented determining the exact position of inland navigation units in the immediate vicinity of the above-mentioned bridges.