The Campo River basin is located on the third plateau of the Parana State or trap plateau of Parana, at the middle portion between the rivers Ivai and Piquiri, southern Brazil, between the coordinates 23 degrees 53 and 24 degrees 10' South Latitude and 52 degrees 15' and 52 degrees 31' West Longitude. The basin has 384 Km(2) area, being 247 km(2) in the municipality of Campo Mourao and 137 km(2) in the municipality of Peabiru, in Parana State. The Campo River is a left bank tributary of the Mourao River, which flows into the Ivai River. The objective of this study was to monitor water quality in the Km 119 River and the Campo River, tributaries of the Mourao River, with monthly collection of water samples to determine pH, temperature, turbidity, biochemical oxygen demand, dissolved oxygen, fecal coliforms, total solids, total nitrogen, ammoniacal nitrogen, nitrite, nitrate and total phosphorus. The results obtained were compared with the indices established by the environmental legislation and applied in the determination of the Water Quality Index (WQI) used by the Water Institute of Parana State, regulating environmental agency. Poor water quality in these rivers presents a worrying scenario for the region, since this river is the main source of water supply for the public system. Results of organic matter, fecal coliforms and total phosphorus were higher than the limits established by Resolution CONAMA 357/2005 to river class 2, specially at downstream of the Km 119 River and the Campo River, due to the significant influence of the urban anthropic activity by the lack of tertiary treatment and also rural by the lack of basic sanitation in this area. Results of WQI of Km 119 River and do Campo River indicated that water quality can be classified as average in 71% and good in 29% of the sites evaluated.
