The paper reviews techniques to assess environmental threat of wastewaters from mining companies. It was proved that the only reliable approach to assessment of technogenic impact on biological systems is application of both biological and non-biological environmental parameters, and which is crucial with obligatory account for their interdependence. Ecological investigation of a section of the Luga River in the impact area of the «PG Fosforit Company», located in the Leningrad Region, was used as an example of environmental impact of a mining company on water ecosystems.