Headwater streams, river modification, heavy-duty vehicles, fish communities, mortality, alpine bullhead, brown trout.

Headwater streams are subjected to a number of interventions. River modification by heavy-duty vehicles for the purpose of repairing and maintenance of technical infrastructure, bridge construction, removal of obstacles from watercourses, gravel mining, or also river restoration is a common commercial practice. Data and information on the impact of heavy duty vehicles during realization of these interventions on fish and other aquatic communities (e.g. on mortality) are very scarce. The aim of the study was to evaluate the rate of mortality of alpine bullhead (Cottus poecilopus) and brown trout (Salmo trutta) and to obtain information on fish movements during these treatments.