E. coli trends in Waikato streams - Exploration of drivers and alternative trend analysis

Report: IS 2022/09

Authors: Simon Woodward, Sandy Elliott, Rob Davies-Colley and Rebecca Stott (National Institute of Water & Atmospheric Research Ltd)

Routine monitoring of concentrations of the microbial indicator Escherichia coli across the Waikato region between 2008 and 2017 indicated that faecal contamination of streams and rivers was generally decreasing. These positive trends may have been due to efforts made to reduce the impact of land use on water quality, such as limiting pastoral intensification, improving effluent management, and excluding stock from waterways by fencing.

More recent monitoring of Waikato streams (2015-2019), however, indicates that concentrations of E. coli are increasing at most river monitoring sites, indicating a deterioration in water quality. This situation is of concern to Waikato Regional Council given the effort expended in policy development and implementation, and the expense that farmers have incurred to meet regional plan requirements. These reported trends are also of concern considering the requirements of the National Policy Statement for Freshwater Management (NPS-FM) 2020, which requires councils to ensure river water quality meets or exceed threshold attribute values (thereby enhancing water quality, including recreational water quality, over time).

Waikato Regional Council wish to better understand the causes of the apparent deteriorating trend in microbial water quality across the region, and commissioned NIWA to undertake a desktop assessment of historical data and provide advice.