Microbial water quality of rivers used for contact recreation in the Canterbury Region

Abstract

Canterbury's freshwaters are highly valued as recreational resources, and are widely utilised for a range of activities including bathing, boating, and fishing. Faecal contamination of freshwater usually arises when the faecal material of human, bird or mammalian waste enters the water. Microbial contamination is of concern to freshwater quality because of the potential for exposure to pathogenic microorganisms in the course of contact recreation. Management of waters for recreational purposes therefore tends to be directed towards protection of public health and has historically relied upon the use of microbiological monitoring for the assessment of suitability for waters for bathing in terms of public health risk.

This study is concerned with the microbial water quality of the Waimakariri, Selwyn, Ashburton and Opihi Rivers during the summer period (1 November to 30 April) when all of these rivers were used for contact recreation in the Canterbury Region. The project assesses whether the above rivers for the summers of 1986/1987 to 1999/2000 complied with the Microbiological Water Quality Guidelines for Contact Recreation based on the SB and C classes of the now repealed Water and Soil Conservation Act 1967. This guideline used faecal coliforms concentrations to assess the microbial water quality. The project also investigated whether temporal and spatial trends had occurred in the microbial water quality in these rivers and suggested some of the possible sources of faecal contamination for these rivers.

The main conclusions drawn from this work are that the Microbiological Water Quality Guidelines for Recreational Waters were not being complied with consistently at the Waimakariri, Selwyn, Ashburton and Opihi Rivers. In addition, while there appeared to be little significant increase in faecal coliform concentration through time, in general, surface water quality tended to decrease downstream as rivers received increasing quantities of contaminants from intensive agriculture, waterfowl, drainage systems, and sewage discharges.