The purpose of the research was evaluate the water quality in two small retention reservoirs also the evaluation of amount of quality indicators retained by the both of them. Water quality studies and analysis of factors determining it were conducted on two small retention reservoirs situated in the Podlaskie Voivodeship: Ciechanowiec, located on the Nurzec River and Bobra Wielka situated on the Biebrza River. The basic physico-chemical parameters of the water reservoirs and of the water supplying them mostly do not exceed the limits for classes I-II. High phosphate concentration, which flow directly into the river supplying the reservoirs, exceed the permissible amounts many times and may be a potential source of contamination of the examined water reservoirs. The yearly increase of researched shows on slow growth of the reservoir degradation level. The reservoirs should be subjected to reclamation as they do not play a role in limiting pollution from the catchment area.