A water quality index for contact recreation in New Zealand

We surveyed the opinions of 16 water quality experts in order to develop a water quality index for contact recreation in freshwaters in New Zealand. T he index was developed by postal surveys using the Delphi method, involving feedback of information to the panel members at each iteration. Determinan ds selected for use in the index were as follows: faecal bacterial indicato rs (faecal coliforms or E. coli), pH, Munsell colour. visual clarity indica tors (black disc visibility or turbidity), and nutrients promoting nuisance growths (filtered BOD,, and dissolved forms of phosphorus and nitrogen). " Sub-index" curves relating suitability-for-use to these water quality deter minands have been developed. The mean ("consensus") sub-index curves can be used to interpret water quality data in terms of suitability-for-use score s. We advocate using the lowest suitability-for-use score for a water as it s overall index value for contact recreation. Thus the water body's suitabi lity-for-use is determined by its "poorest" characteristic. The index is no w ready to be tested by water managers for its utility in state-of-environm ent reporting.