Brazil has a large potential for aquiculture, which is listed as an important alternative to rise fishing production in the country. The activity is developed mostly in open systems (reservoirs), and control and prevention actions take important place due to the difficulty to reduce the environmental impacts of this activity on water, which must be preserved in order to guarantee its multiple uses. In this study, water quality monitoring and evaluation was carried out in Ribeirão Can-can, where are installed three units of fish farms in cage system located at Ilha Solteira Reservoir, at the city of Santa Clara d’Oeste - SP. The analyses needed for the research were carried monthly from September 2016 to September 2017 in four strategic sites of the water body. As of the results of physical, chemical and biological tests a comparative analysis was made with CONAMA Resolution nº 357/05 standards for fresh waters class 2 and applying the Water Quality Index (WQI) from CETESB (Environmental Company of the State of São Paulo) in order to obtain a quality classification level of the monitored water body and correlate it with possible sources of pollution. With the results of WQI observed, the water quality was classified between good and great. Despite it, were found high phosphorus concentrations in all samples, varying between 0,07 mg/L and 0,96 mg/L. As so, the waters of Ribeirão Cancan deserve attention by constant monitoring and evaluations because of its high potential to eutrophication.