The role of Angara Biological Station in the study of ecological state of Angara River and Bratsk Reservoir during its forming until the present time is presented. The results of investigations of primary production, phyto-, bacterio-, zooplankton, zoobenthos and ichthyofauna of Bratsk Reservoir allowed to establish general features and peculiarities of their forming. The income of waste waters leads to decline of species reachness of hydrobionts. The most dangerous for the shore communities of reservoir is the sufficient decrease of water level in under-ice season.