[Biological monitoring of water quality]

The degree of purity of surface waters can be seen from investigations on the communities of life of plant and animal organisms. A great number of organisms characteristic of certain degrees of pollution were classified in the "saprobic system", which is still valid. As a supplement to the chemical water analysis, the bio-ecological test is an optional method for characterizing the quality of waters--as, for instance, in the case of the river Lippe.