Polychlorinated biphenyls (PCBs) are universal environmental contaminants that have attracted great concern because of their worldwide distribution, persistence in the environment and possible harmful effects. Recycling old objects or materials containing PCBs and former disposal sites, could potentially contaminate surface waters. According to previous studies, it appears that in some Swiss rivers, the concentration of PCBs in fish were above the limits proposed by EU, indicating a contamination which is considered to be "very high". It was therefore decided to conduct an investigation along two of them, the “Venoge’ and the ‘Birse’ Rivers, in order to detect potential sources of pollution contaminating them. A simple, rapid and easy method using passive samplers of Low-density polyethylene (LDPE), known to adsorb PCBs, has been established. It is therefore an accessible technology and requires no power source or specialized equipment in situ. The passive samplers were placed over 2 iron bars at each measurement site. They were fully immersed during the duration of the experiment, typically 4 to 6 weeks. Once out, PCBs from the LDPE samplers were extracted using dichloromethane, purified by adsorption chromatography and analysed by gas chromatography (GC-ECD). Results show the great interest of LDPE passive samplers in the identification of sources of contamination in rivers. One industrial site, a former landfill and a wastewater treatment plant receiving waters from an industrial zone were pointed out as sources of PCBs in both rivers.