Swimming-Associated Illness and Recreational Water Quality Criteria

Abstract

There is a measurable risk of acute gastroenteritis associated with swimming in marine waters contaminated with human fecal wastes to levels that would be aesthetically acceptable. The enterococcus level in the bathing water is the best single measure of its quality relative to the risk of swimming-associated, pollution-related infectious disease. Three mathematically expressable indicator-illness relationships (criteria) are available from which recreational water quality guidelines can be extrapolated from the criteria once a decision has been made as to the acceptable risk of illness. The recently revised USEPA recreational water quality criteria and guidelines reflect this regulatory approach. A model is presented for the regulation of water quality which defines decision-making and actions by federal and local agencies as well as resource users. This model requires the ability to predict illness rates from monitoring data. Three equations, each corresponding to one of the criteria, are available for doing so. Concept and supporting epidemiological data indicate that the criteria do not apply to situations in which the sources of contamination are the fecal wastes from small numbers of individuals (e.g. boat wastes, the bathers themselves) or from lower animals (e.g. stormwater run-off). Differential die-off of viral pathogens and the bacterial indicator during wastewater chlorination and protracted residence in marine waters may also confound the use of the criteria in specific situations.