River water quality in Tāmaki Makaurau: Annual data summary 2025

Author:

Rhian Ingley

Source:

Auckland Council Environmental Evaluation and Monitoring Unit, EEMU

Publication date:

2025

Topics:

Environment

Auckland Council's online interactive Water Quality and River Ecology Data Explorer presents State of the Environment (SoE) monitoring data for rivers, lakes, groundwater and the coast. River water quality can be compared across the region, by season, and over time.

This report provides a summary of river water quality monitoring results for July 2020 to June 2025 and includes the first information summary for 12 sites added to the programme in 2022.

Key messages

Land use and seasonal patterns

Water quality was generally poorest in urban streams and best in native forest streams.
Streams within native forest catchments had smaller fluctuations in temperature, pH, and dissolved oxygen levels and lower concentrations of nutrients and faecal indicator bacteria compared with other streams, and metal contaminants were rarely detected.
There were clear seasonal patterns in several water quality measures although these patterns can vary between locations and peak concentrations may occur in different seasons.

12 new sites expand representation

New sites were added to improve regional network representation across land cover and biophysical classes, with a focus on wider Kaipara and Manukau Harbour areas and future urban areas.
Kaipara - Three new sites in the Hōteo River catchment including two large rural tributaries, one of which is within a future urban area the Kumeū River catchment. The third site (Waiwhiu Stream, in Dome Valley) is a lower impact site, the least-impacted local reference site available in the Kaipara area.
Manukau - Four new sites in the wider Otūwairoa Stream/Slippery Creek catchment across a broader pressure gradient, that will provide a baseline for future urban development. Two new sites in the southern Pukekohe area which may be influenced by groundwater nitrate contamination. In combination these provide better coverage of the Manukau catchment.
Hauraki - One new site in Ōrewa and one in the Mahurangi River catchment, both near future urban areas.

Auckland Council, December 2025