
Changes in aquatic ecosystems are resulting from human activities, for example domestical, agricultural and industrial discharges. Nowadays, conventional physical-chemical parameters are not suitable for hazard assessment anymore. The Quati River (Paraná, Brazil) is a very important river for the population of Cascavel city, and in 2011 was contaminated by a leak of industrial sewage. Since then, no environmental study was made on this river. Thus, this study aimed to evaluate the status of the Quati River according to genetic parameters: micronuclei (MN) and chromosomal aberrations (CA) frequencies and the mitotix index (MI); using the Allium cepa test in two points of the river (P1 and P2). Distilled water was used as negative control (NC) and MMS as positive control. Were observed statistically increasing in all parameters compared to NC (p < 0.05). Shockingly, a fold-increase of 7.97 in P1 and 4.23 in P2 were observed in MN frequencies. We observed that the Quati River is contaminated and that this contamination is possible caused not only by the industrial sewage leak in 2011, but by constantly sewages dumped into the river. We suggest more surveillance on the river and the continuity of environmental studies for monitoring.