Since the political change and due to high market prices for gold the mining sector has considerably grown in Mongolia and has become one of the most important economical sectors. With increasing mining activities the mining related environmental problems also increased, especially those, which are caused by open placer gold mining. Placer gold deposits are located in the alluvial sediments of river fl oodplains and the exploitation of these deposits often induces severe impacts to river ecosystem and its different components. In this paper we describe the effects of open placer gold mining on diatoms, benthic invertebrates and fi sh in four rivers in the north-east of Mongolia. Our fi ndings are based on a comparative analysis of these biocoenotic groups in pristine and mining affected river sections, taking into account also abiotic habitat characteristics. Our analyses revealed that placer gold mining causes multiple stressors acting on different trophic levels. The biocoenotic groups under investigation reacted differently against stressors, and we indentifi ed a wide range of direct and indirect effects. These fi ndings are new for Mongolia and are essential to defi ne adapted and successful strategies for an ecologically based management and monitoring of open placer gold mining pressures and ecological impacts.