River ecology current state and trends in Tāmaki Makaurau / Auckland 2024. State of the environment reporting. 

See also

Data files, state and trends. Appendix A

Executive summary

This report is one of a series of publications prepared in support of Te oranga o te taiao o Tāmaki Makaurau – The health of Tāmaki Makaurau Auckland’s Natural Environment in 2025.

This report presents the current state of river ecology in Tāmaki Makaurau / Auckland, assesses it against the relevant National Policy Statement for Freshwater Management (NPS-FM) 2020 National Objectives Framework (NOF) ecosystem health attributes, and explores how scores for the metrics used to assess river ecological health have changed over the past 10 to 15 years (the trend period for each metric depends on the dataset available).

The ecological health of rivers and streams can be affected by a variety of factors, including the types of land use activities within their catchments, diffuse and point-source discharges, erosion, as well as climatic variability.

Auckland Council’s River Ecology Monitoring Programme involves sampling aquatic macroinvertebrates (stream insects) at 63 sites throughout the Auckland region on an annual basis, as well as undertaking Stream Ecological Valuation (SEV) assessments that incorporate measures of biophysical and habitat quality. Seven of these 63 sites are native forest reference sites, which provide a baseline for ‘undisturbed’ catchments against which sites within different land-uses can be compared.

This field data is then used to calculate several metrics, including the Macroinvertebrate Community Index (MCI), Quantitative Macroinvertebrate Community Index (QMCI), and SEV score.  

Freshwater fish monitoring has also been undertaken at 44 of the river ecology monitoring sites using standardised sampling methods to gather data on fish communities. This data has been used to calculate a fish Index of Biotic Integrity (fIBI) score for each site, which provides an indication of the health and intactness of the resident fish fauna. Three native forest reference sites are sampled annually, with the remaining fish sites sampled on a rotating basis once every two to three years.

Sampling reference sites regularly alongside other land use classes helps account for seasonal variability in macroinvertebrate monitoring as it allows researchers to distinguish natural fluctuations from the effects of specific land uses or disturbances like drought. For example, if drought impacts are present in both reference and impacted sites, the differences between them can be attributed to the land use, while the shared impact can be attributed to the drought. 

The macroinvertebrate, fish, and SEV metrics are used both separately and together to enable us to evaluate the overall ecological health of rivers throughout the Auckland region.

The current state was assessed based on the five-year period from 1 July 2019 to 30 June 2024. Trends were analysed over different timeframes depending on the size of the datasets available for each metric. For the MCI and SEV metrics, trends were assessed over a 15-year period, from 2010 to 2024 inclusive. For sites where 15 years of data were not available, and for the Average Score Per Metric (ASPM) and Quantitative Macroinvertebrate Community Index (QMCI) metrics, trends were determined over a 10-year period, from 2015 to 2024 inclusive.

The key findings from this report are similar to those from previous river ecology state and trends reports for Tāmaki Makaurau. All river ecology metrics showed a general decline in relation to increasing intensity of land use within the catchment, with reference sites located in native forest catchments having the highest ecological values and sites in urban catchments the lowest.

Over half of the monitoring sites were found to fall below the ‘national bottom line’ defined in the National Policy Statement for Freshwater Management (NPS-FM) for all three macroinvertebrate metrics while only 24 per cent of sites did not have at least one metric that fell below this level.

Across all metrics the number of improving and degrading trends were roughly equal (47 per cent improving cf. 43 per cent degrading) with 10 per cent having no defined trend either way. When evaluated in terms of land cover categories, more streams within rural catchments were improving than degrading, but there were high proportions of sites in native forest and urban catchments experiencing degrading trends.

Analysis of both state and trend metrics revealed that, not only were many of the sites that are currently in the poorest ecological condition continuing to degrade, but that two native forest reference sites are also showing degrading trends. This result cannot be explained at present, and an in-depth analysis of potential drivers is outside the scope of this report. Since these reference sites are supposed to act as a benchmark for stream ecological values in the region, further investigation will be required to determine the cause of these degrading trends.

Within the period covered by this report Auckland Council also established a region-wide Fish Monitoring Programme, starting in 2020. Although the dataset for this programme is not yet large enough for a full state and trends analysis, the initial results are presented in this report. These showed that 52 per cent of sites scored within the top NPS-FM band, while none fell below the national bottom line value. Overall, this indicates that fish populations within Auckland streams appear to be relatively intact and diverse. The collection of additional fish monitoring data over the coming years will enable a clearer picture to be established of the health of fish communities throughout the region. This will also allow for more powerful analyses to be undertaken on the dataset and a greater range of fish community metrics to be reported on in future.

During the period covered by this state and trend analysis the Auckland region suffered its most extreme rainfall event on record, the Auckland Anniversary Day floods in late January 2023, followed by Cyclone Gabrielle in early February 2023. The impact of these extreme weather events on the stream ecology values at our monitoring sites are explored in detail as a stand-alone case study within this report. Surprisingly, there were no significant ecological impacts detected in the macroinvertebrate metrics when comparing post-flood data to that collected prior to the flooding. This suggests that macroinvertebrate communities exhibit a high level of resilience to stochastic weather events, with populations able to return to pre-impact levels within a year.

Some ecological degradation attributable to the flood events was detected in the SEV scores, with statistically significant differences detected when comparing pre-flood to post-flood data. This is because the SEV methodology incorporates measures of stream biophysical and hydraulic functions in addition to the biological functions measured using macroinvertebrate metrics, which illustrates the benefit of incorporating a more holistic method of evaluating stream ecological values.

The findings within this report can be used to satisfy the regulatory requirements for Auckland Council to monitor environmental state and trends as required by the NPS-FM, to inform the effectiveness of policy initiatives, strategies and ecological restoration activities, and to support other monitoring and research programmes throughout the region. 

Auckland Council technical report, TR2025/28

September 2025

See also

Data files, state and trends. Appendix A

Te oranga o te taiao o Tāmaki Makaurau. The health of Tāmaki Makaurau / Auckland’s natural environment in 2025. A synthesis of Auckland Council’s state of the environment reporting