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. Groundwater quality data can be compared across the region, between aquifers and over time.¹

This report provides a summary of coastal water quality monitoring results for July 2020 to June 2025.

Key messages

Freshwater inputs drive coastal water quality

• Sites in, or near the entrance of, narrow inlets or rivers in upper harbour and estuary experienced the strongest freshwater influence and were the most sensitive to land-derived water quality effects. Water quality was poorest at these sites and generally better at sites with decreasing freshwater influence. Water quality was good towards central and outer harbour sites, with best quality in exposed open coastal sites.

Nutrients are high in some locations

• Nutrient concentrations were higher in the upper Waitematā Harbour tidal creeks, at Panmure Bridge in the Tāmaki Estuary, the Kaipara River Mouth, and in the Manukau Harbour. More targeted monitoring will be required to better understand ecological impacts of nutrients in our estuaries.

Cyclone Gabrielle affected Kaipara Harbour water quality

• Sampling in the Kaipara Harbour in February 2023 captured some of the effects of Cyclone Gabrielle on harbour water quality. This influenced salinity, temperature, dissolved oxygen and nitrogen at some sites; however effects of the cyclone were not as obvious in other harbours.

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1. This does not include the detailed statistical analysis that is required to assess trends in water quality over time and is reported in our five-yearly State of the Environment reports.

Auckland Council, December 2025

See also

Water Quality and River Ecology Data Explorer. Website for water quality data.

     Coastal water quality

Water quality and river ecology data explorer user guide and methodology. Supplementary report

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Groundwater quality in Tāmaki Makaurau: Annual data summary 2025

Lake water quality in Tāmaki Makaurau: Annual data summary 2025

River ecology in Tāmaki Makaurau: Annual data summary 2025

River water quality in Tāmaki Makaurau: Annual data summary 2025