flavobacterium psychrophilum, the causative agent of coldwater disease, affects salmonid fish in aquaculture operations worldwide and causes skin lesions which if left untreated results in spinal deformities, spiral swimming and eventual death. currently, there are no available vaccines for coldwater disease. the use of antimicrobials is limited to reduce the potential development of antibacterial resistance in bacteria. this study examined the association between f. psychrophilum and water quality parameters (specifically dissolved oxygen and nitrite) to determine what associations would be best to develop alternative management techniques. in addition, this study investigated the impact of ultraviolet disinfection on planktonic bacteria concentrations and biofilm development in the treatment of land-based aquaculture effluent. the study locations were two commercial partial recirculation rainbow trout oncorhynchus mykiss (walbaum) aquaculture facilities located in coldwater, on and new dundee, on. at the coldwater fishery, water samples were collected monthly from march 2013 to october 2013 from 6 sampling locations and water quality parameters and planktonic bacterial densities were measured. at lyndon fish hatchery, in new dundee, samples were collected from june 2014 to august 2014 from 4 sampling locations and to measure water quality parameters, planktonic bacterial densities, biofilm bacterial densities and uv efficacy on planktonic bacterial load. a field study of biofilm growth was investigated by suspending glass slides on either side of a uv reactor connected to the effluent flow. results indicated that the abundance f. psychrophilum did not demonstrate a clear association with water quality parameters. the water quality parameters that had the strongest correlations with f. psychrophilum at coldwater fishery were po4, ph and nh3. the water quality parameters that had the strongest correlations with f. psychrophilum at the lyndon fish hatchery were no2-, tkn and temperature. the concentration of biofilm heterotrophic bacteria and f. psychrophilum remained similar at the uv influent and uv effluent areas despite reductions in the planktonic bacterial density.