The results of an environmental perception study about a contaminated watercourse in Guadalajara Jalisco, Mexico are presented. Percept and opinions of residents were collected by direct interview from a random sample of 370 out of 8 900 dwellings and statistical reliability of 95%. Main results highlighted complains about sewage dumping and related displeasing odor (39.3%), as well as the presence of mosquitoes (17.6%) as disease vectors. At most impacted sites (P3, P4, P6, P8) common reported signs and symptoms were irritation to organs of the respiratory system and headache. Thus, finding a very significant association (chi-square test, P<0.0000) among prevailing environmental conditions and reported symptoms at 95% confidence interval. Finally, 90% of interviewee qualified the channel´s environmental quality as very bad, since the benefits they can get from a natural stream like landscape beauty, microclimate regulator or water supply, are limited by the unhealthy state of water.