The biological survey of the reservoir Chirita - Iasi was established on a three months basis. 7 sampling sites were fixed in order to offer data about the general situation of the reservoir’s benthic fauna. A series of ecologic indicators were calculated in order to characterize the biocoenosis: analytic (abundance, constancy, and dominance) and synthetic (ecological significance index).In the three months of survey a total number of 2322 specimens belonging to 16 species were found.The best represented species in the biological samples was Chironomus plumosus with 1064 specimens of larvae and a percentage of 45.82%.