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 lake water quality monitoring results for July 2020 to June 2025.

Key messages

Most lakes in Auckland are in poor health

• 11 out of 13 (85%) of the monitored lakes in the Auckland region were in poor or very poor health.

Lake health differs between lake types

• Shallow, polymictic (well -mixed) lakes generally have poorer water quality than deeper, seasonally stratified lakes (where the water separates into layers between October and May).
• Concentrations of nutrients, algae and turbidity were generally higher in the polymictic lakes.

Stratification results in low oxygen and nutrient release from sediments

• Seasonally stratified lakes have prolonged periods with low oxygen and high nutrient concentrations in the bottom waters, where redox conditions allow for potential nutrient release from lakebed sediments (internal loading).

Risks to human health were low

• Cyanobacteria counts were low in publicly accessible lakes, but higher in other lakes.
• There are low levels of E. coli across all lakes in the region, with infrequent episodic high results in some lakes.

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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.

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

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Coastal water quality in Tāmaki Makaurau: Annual data summary 2025

Groundwater 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