JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION VOL. 38, NO. 1 AMERICAN WATER RESOURCES ASSOCIATION FEBRUARY 2002 DISCUSSION' "Oregon Water Quality Index: A Tool for Evaluating Water Quality Management," by Curtis G. Cude2 David G. Smith, Robert J. Davies-Colley, and John W Nagels3 Cude (2001) discusses the development of the Ore- gon Water Quality Index (OWQI) and demonstrates how this index can be used to improve comprehension and communication of complex water quality issues to the "general public and policy-makers." As regards the use of water quality indexes, we have no issue and we fully support the intent of the paper. However, there are some aspects of the OWQI that we consider unsound. We believe that agencies planning to use this, or a similarly-derived index system, need to be aware of certain problems. First, the classification scheme in the OWQI (scores less than 60 "are considered" very poor; 60 to 79, poor; and so on up to 90 to 100, excellent) was apparently introduced after the development of the subindex curves. Each subindex curve should have been developed with this classification scheme clear in the minds of the panel so as to guide their curve positioning. This would ensure that a subindex value of say, 60, for dissolved oxygen would be equivalent to a value of 60 for all the other analyses included in the index, in terms of water suitability-for-use. It is unclear how analytical values were translated into subindex values in the development of each subindex curve. Second, the precise method of subindex curve development is not clear. A panel of experts was used "to choose variables and to determine weighting fac- tors for each variable" in the development of the origi- nal OWQI, but it is not stated whether such a panel was used to derive the subindex curves. We have found in our studies (e.g., Smith, 1990; Nagels et al., 2001) that the opinions of "experts" can vary widely and it is dangerous to accept the advice of a single such expert. Typically the pooled responses of several experts show considerable diversity. However the average curve from a panel containing perhaps 20 experts is much less likely to be affected by idiosyn- cratic "outlying" opinions, leading to a superior final product (i.e., a robust index) In the "Uses and Limitations" section, the paper clearly states: "The OWQI aids in the assessment of water quality for general recreational uses (i.e., fish- ing and swimming)." One of the most important fac- tors in human recreation, including swimming, is visual perception of the water body (see, for instance, Smith et al., 1995, for a brief review of this topic and the relevance of water clarity and hue). Therefore any index purporting to assess suitability for swimming must account for these variables. In more general terms, aesthetic values placed on water bodies are nearly always applicable, no matter which recreation- al use is considered. For fishing, water clarity is paramount not only as regards sighting of the lure by fish, but also inasmuch as it affects the aesthetic experience associated with trout fishing. For trout fishers (and the index is stated to be protective of cold water fisheries), inclusion of water clarity is vital. The OWQI ignores visual aspects and therefore cannot claim to be comprehensive for the uses stated. We are unclear as to the relevance of some of the analytes chosen, for instance, the use of ammonia+nitrate nitrogen when oxygen removal is accounted for with BOD, and eutrophication is 1Djscuss ion No. 99051D of the Journal of the American Water Resources Association. 2Paper No. 99051 of the Journal of the American Water Resources Association 37(1): 125-137. 3Respectively, Director, Aquatic Studies, New York City Department of Environmental Protection, 465 Columbus Avenue, Valhalla, New York 10595; and Assistant Principal Scientist and Senior Technical Officer, National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand (E-Mail/Smith: smithd@water.dep.nyc.ny.us). JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 313 JAWRA