Peru is a country with a high mining potential. Among the regions with the highest presence of such extractive activity is Ancash; despite all the economic benefits provided by mining, it is necessary to remediate the environmental impact caused by the operations. Therefore, this research proposes the application of a grey clustering method called Center Point Triangular Whitenization Weight Function (CTWF), which is based on fuzzy logic, as an assessment mechanism to determine the water quality of the Santa river basin, located in the mentioned region, in which mining, agricultural and animal husbandry activities are developed in parallel. This methodology was applied to perform the analysis of the monitoring points recorded in the water quality reports issued by the National Water Authority in 2 different years: 1997 and 2014; with the objective of having an idea of how the water quality had evolved between those years. The results showed an evident improvement in the water quality of the basin, this could be due to different reasons, among them, the emerging environmental responsibility of the companies that carry out extractive activities. The results obtained and the methodology applied can be useful for the national environmental control authorities, as it is a tool that can provide information and help in decision making.