Multivariate analysis of an extensive dataset based on the macroinvertebrate fauna of surface waters in the province of Overijssel (The Netherlands) has resulted in the description of 42 site groups. These include springs, streams, rivers, canals, ditches, pools and lakes. The site groups are recognised on the basis of environmental variables and the abundance of organisms. For each group only a recognisable centroid and a limited range of variation is given; no clear boundaries are described between the groups. These site groups and their environment are defined as cenotypes. The cenotypes are mutually related in terros of key factors which represent major ecological processes. The cenotypes and their mutual relationships form a web which offers an ecological basis for the daily practice of water and nature management. The web allows the development of water quality objectives, provides a tool for monitoring and assessment, indicates targets and guides the management and restoration of waterbodies. The web is included in a software package named EKOO. The main modules in this package are (1) the assignment of a newly sampled site to one of the cenotypes, (2) the characterisation of a new sample in terms of diversity and biotic features, and (3) the option to choose a target for a newly sampled site and to establish a set of measures to reach this target.