This study was an investigation into the relationship of bacterial water quality and the incidence of illness amongst lake and chlorinated pool swimmers. During the summer of 1972 three groups of swimmers were surveyed: 1. Lake Okanagan swimmers who swam at the Kelowna City Park beach 2. Ogopogo Aquatic Team who swam at the same beach 3. Chlorinated swimmers who swam at an unheated community pool The swimmers ranged in age from six to sixteen and were surveyed for upper respiratory illness, gastroenteritis, otitis externa, shistosomiasis and conjunctivitis. The lake water, proximal creeks, and chlorinated pool were sampled throughout the swimming season for the fecal contamination indicators; fecal coliforms and fecal streptococci. Bacterial water quality of the creek varied with the effluent input and quality of the lake water varied with inflow from the creeks and swimming density. The flake fecal coliform counts generally remained below 200 organisms per 100 milliliters. The lake fecal streptococci counts were slightly higher than the fecal coliforms and more responsive to swimming density. In the chlorinated pool samples fecal coliforms were not present while fecal streptococci counts ranged up to 168 organisms per 100 mis. Contamination at all sites was of both human and animal origin. Total illness incidence was highest amongst Hake Okanagan swimmers and lowest amongst the Ogopogo Aquatic team swimmers. The most distinctive illness difference observed between lake and chlorinated pool swimmers was the incidence of otitis externa. For Lake Okanagan swimmers the incidence was 17.82 per 1000 person hours water exposure, for the Ogopogo Aquatic Team the incidence was 16.48 and for chlorinated pool swimmers incidence was only 0.67. It was surmised that the causative organism for the auditory dermatitis was Pseudomonas aeruginosa and its presence was verified in the lake water and streams and negated in the chlorinated water. For lake swimmers the correlations between incidence of illness and lake fecal indicator counts were significantly positive for upper respiratory infections, gastroenteritis and otitis externa. The correlation coefficient exhibited between otitis externa of lake swimmers and the fecal streptococci counts was .866. Throughout statistical analysis fecal streptococci counts displayed stronger positive correlations with illness incidence than the fecal coliform data. For chlorinated pool swimmers the illness patterns did not significantly correlate with fecal streptococci counts. It was recommended that fecal coliforms alone were an inadequate index of recreational water quality. It was also suggested that Ps. aeruginosa warranted further research as a potential water affiliated pathogen and water quality index. / Science, Faculty of / Zoology, Department of / Graduate