The Racecourse Wetland in Wyong, New South Wales, was used for twenty years (1968–1988) as a site for disposal of secondarily treated sewage effluent. The area of the wetland is 90 ha and the average amount of effluent received was 1.7 ML/day. A nineteen-month study (June 1986-January 1988) was undertaken in order to determine the efficiency of pollutant assimilation in the wetland, with particular reference to plant nutrients. The wetland was sampled at approximately fortnightly intervals, at six different sites at various distances from the oxidation pond outlet. The first downstream sampling site was 650 m from the oxidation pond, where average concentrations of ammonia and total phosphorus were reduced by more than 99 percent to 59 μg/L and 39 μg/L respectively. Concentrations of nutrients in samples of effluent from the oxidation pond varied with season. Average summer concentrations for ammonia were 30 mg/L compared with 6 mg/L for winter. The corresponding total phosphorus concentrations were 12 mg/L and 9 mg/L. Downstream of the first sampling station the wetland seemed to function as a mild nutrient source rather than sink. However, the levels of nitrogen and phosphorus reaching the nearby Wyong River were very low, with phosphate and total Kjeldahl nitrogen levels only slightly higher than those already in the river.