An alternative biological water quality index

A biological water quality index based on the wholly subjective assessment of stream biota is proposed. Biological sample data from a wide variety of sites in the North West of England were assessed for productivity (Np), diversity (ND) and quality (NQ). Performance of these indices was examined. ND was well correlated with objective indices in routine use and showed similar percentage errors. There were good correlations between operator and similarities in both mean levels and ranges between operators. It is proposed that this approach is worthy of consideration as a preliminary means of assessing and reporting quality for whatever purpose as defined by the user. It could serve as an adjunct to more objective methods, but would not replace them.