Human growth since the Industrial Revolution and the post-war period has put drastic pressure on natural resources. In Alumínio - SP, the large urban concentration of this municipality is densely packed into the sub-basin of the Bugre stream, greatly compromising the quality of its waters, especially in the urban perimeter. In this sense, environmental diagnosis is fundamental for monitoring and understanding the state and quality of the natural resources exploited and for helping to make decisions. Over the course of a seasonal year, this study carried out a diagnosis of water quality at three points in the Bugre stream, using parameters included in CETESB's IVA (Water Quality Index for the Protection of Aquatic Life and Aquatic Communities) and IQA (Water Quality Index). The first point is located at the source (an area with native vegetation) and the second and third are located on the urban perimeter. The parameter data was statistically analyzed using Principal Component Analysis (PCA). According to the evaluations of the points, there were notable variations in water quality between the three points analyzed.