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Seasonal and temporal variation in water quality in New Zealand rivers and lakes

Publication date:  May 2019
Publication reference number:  CR 350

This report analyses seasonal patterns in river and lake water quality across New Zealand, using data from 2013–2017.

River water quality showed significant differences between summer and winter, and these patterns were different in rivers with different types of land cover. For example, regions dominated by high-intensity agriculture typically had poorer clarity, turbidity, and nutrient concentrations in winter than in summer.

This study supports the common perception that river water quality is poorer in winter, with the exception of E. coli, which is used to evaluate human health risks associated with contact recreation. E. coli concentrations were significantly higher in summer compared to winter.

This study also presents an assessment of the variation in water quality between night and day, using the Tukituki River as a case study. This data shows strong fluctuations in pH, dissolved oxygen, and nitrate-nitrogen concentrations between night and day.