Freshwater Data Shown Through Best-Practice Guidelines

This map displays modelled river nitrogen data across rivers in New Zealand using the Australian and New Zealand guideline values (2025). It brings together the location of Ngāi Tahu marae and waterbodies identified in the Freshwater Statement of Claim to contextualise environmental data with places of cultural significance.

Nitrogen is an important nutrient to manage because it harms freshwater systems in excess concentrations: it can be toxic to aquatic life and enable algal blooms that degrade aquatic habitat quality and natural processes. Viewing these datasets together encourages us to think holistically about how freshwater conditions are impacting communities across the takiwā.

Elevated nitrogen levels in our waterways are largely driven by land-use practices, primarily via leaching from intensive agriculture. The proportion of land in the upstream catchment that is affected by human activity is superimposed on the map. Shifting the slider enables a comparison between freshwater nitrogen levels and land-use intensification. Our Freshwater Health page explores these challenges in more detail.

This map draws on renewed nitrate toxicity guidance to provide a detailed view of the regions where freshwater species could be significantly impacted. The need to better protect aquatic ecosystems becomes more apparent when using this guidance to visualise freshwater data, as it highlights a starker situation than previously known. Continuing to adopt strong and reliable evidence helps to ensure robust frameworks, durable policies and sustainable water systems for everyone.

Te Kura Taka Pini envisages a future where environmental information is brought together in a way that reflects our shared values, the true health of waterways and enables Ngāi Tahu rangatiratanga for generations to come.

This map displays modelled river nitrogen data across rivers in New Zealand using the Australian and New Zealand guideline values (2025). It brings together the location of Ngāi Tahu marae and waterbodies identified in the Freshwater Statement of Claim to contextualise environmental data with places of cultural significance.

Data sources: Stats NZ. (2026). River water quality – nitrogen: Data to 2024. Modelled median NNN concentration for 2020–2024, modelling by Earth Sciences New Zealand.

Guideline values: Classes incorporate the New Zealand nitrogen baseline threshold from Morgenstern & Daughney (2012) and the ANZG (2025): Toxicant default guideline values for aquatic ecosystem protection: Nitrate in freshwater (soft water).