Coal power plants constitute an important component of the energy mix in many countries. However, coal power plants can cause several environmental risks such as: climate change and biodiversity loss. In this study, a tool has been proposed to calculate the environmental impact of a coal-fired thermal power plant in operation by using multicriteria scoring and fuzzy logic method. We take into account the following environmental parameters in our tool: CO, SO2, NOx, particulate matter, fly ash, bottom ash, the cooling water intake impact on aquatic biota, and the thermal pollution. In the proposed tool, the boundaries of the fuzzy logic membership functions were established taking into account the threshold values of the environmental parameters which were defined in the environmental legislation. Scoring of these environmental parameters were done with the statistical analysis of the environmental monitoring data of the power plant and by using the documented evidences that were obtained during the site visits. The proposed method estimates each environmental impact factor level separately and then aggregates them by calculating the Environmental Impact Score (EIS). The proposed method uses environmental monitoring data and documented evidence instead of using simulation models. The proposed method has been applied to the 4 coal-fired power plants that have been operation in Turkey. The Environmental Impact Score was obtained for each power plant and their environmental performances were compared. It is expected that those environmental impact assessments will contribute to the decision-making process for environmental investments to those plants. The main advantage of the proposed method is its flexibility and ease of use.