To provide an environmental evaluation method of water area which expresses natural environment in a water area numerically and by a graphical expression by using benthonic animals and enables the easy and objective evaluation of the natural environment.

The benthonic animals are quantitatively collected in the water area of survey object, the species of the collected benthonic animals are identified and the number of individuals is counted. Subsequently, the benthonic animals are classified by using the correspondence of the name of the species and the life style, the number of the species and the number of the individuals with respect to the life style are cumulated and expressed numerically, the constitutional ratio of the life style is divided into the number of the species and the number of individuals and both are overlapped with each other and are expressed graphically. Thereby, the water area environment in a collection spot is visually expressed and evaluated. Further, by comparing the data of the water area with the conventional data, the natural environment of the water area is evaluated.