The Environmental Evaluation System (EES) is a methodology for conducting environmental impact analysis. It was developed by an interdisciplinary research team and is based on a hierarchical arrangement of environmental quality indicators, an arrangement that classifies the major areas of environmental concern into major categories, components, and ultimately into parameters and measurements of environmental quality. The EES provides for environmental impact evaluations in four major categories: ecology, environmental pollution, esthetics, and human interest. These four categories are further broken down into 18 components and finally into 78 parameters. The EES provides a means for measuring or estimating selected environmental impacts of large-scale water resource development projects in commensurate units termed ‘environmental impact units’ (EIU). Results of using the EES include a total score in EIU ‘with’ and ‘without’ the proposed project; the difference between the two scores is one measure of environmental impact. Environmental impact scores developed in the EES are based on the magnitude of specific environmental impacts and their relative importance. Another major output from the EES is an indication of major adverse impacts called ‘red flags’, which are of concern of and by themselves. These flags indicate ‘fragile’ elements of the environment, which must be studied in more detail.