The first results of the biological and hydraulic monitoring programme carried out during the sediment flushing of an Alpine Italian reservoir are presented. The flushing and the monitoring activities were planned and executed by several private and public subjects, including the hydroelectric company in charge of the reservoir management (AEM S.p.A.), local environmental agencies, an angler association, a company of environmental consultancy (Graia S.r.l.), the Insubria university. The Italian normative requires that the sediment removal from a reservoir should follow a Reservoir Management Plan compiled by the reservoir manager (which is also in charge for the execution of the flushing operation). Difficulties arise in planning such operations since no threshold limits for the suspended solid (SS) concentration of the outflow waters are defined at National level. For this reason the present research was addressed to provide experimental evidence of the SS effects on the aquatic biota present in the creek downstream of the flushed reservoir, aiming at establish ecologically-based threshold limits of SS concentration. A second objective of the research was to verify how much the effluent SS concentration could be controlled by means of technical operations for flushing management.