Freshwater Health

Freshwater is central to life in the Ngāi Tahu Takiwā — environmentally, culturally, economically and socially. It connects people, land and ecosystems, shaping both environmental health and cultural identity. The significance of wai is further underscored by the fact that around two-thirds of New Zealand’s surface water (measured by surface area) and more than 70% of its groundwater lie within the Ngāi Tahu Takiwā.

Yet the health of these waterways is increasingly under threat. Decades of over-extraction, irrigation and intensive land use have increased contaminant runoff and reduced flows in many rivers. In turn, water quality has declined, aquatic ecosystems have degraded and, in some catchments, drinking water is no longer safe.

This deterioration challenges New Zealand’s "clean, green" image and has intensified legal, political and cultural debate over how freshwater should be managed. For Ngāi Tahu however, the impacts run deeper than environmental change alone. The degradation of wai undermines the exercise of kaitiakitanga (guardianship), disrupts mahinga kai (customary food gathering) and erodes rangatiratanga (tribal authority) within the takiwā.

Over the past three decades, water quality across the Ngāi Tahu Takiwā has deteriorated dramatically. This decline has occurred despite the existence of a legislative framework intended to manage environmental effects. It reflects the cumulative impacts of intensive land use, poor regulation and limited enforcement.

Intensive dairy farming has been one of the most significant contributors. The total number of dairy cattle in the South Island has risen by 829% since 1990. This expansion has resulted in more irrigation, greater fertiliser application and higher volumes of effluent entering waterways.

Elevated nitrate concentrations in groundwater have followed, with consequences for both ecosystem and human health.

The effects are visible in lakes and rivers throughout the takiwā. An example is Te Waihora / Lake Ellesmere, classified as hypertrophic or of very poor water quality. The lake is in a persistent degraded state, with a high health risk throughout the year from exposure to toxic cyanobacteria.

When freshwater quality deteriorates, the health of aquatic ecosystems declines and the safety of drinking water becomes compromised. For Ngāi Tahu whānau, this degradation also restricts the ability to access and engage with freshwater in ways that uphold tikanga and fulfil kaitiakitanga responsibilities.

Across the Ngāi Tahu Tākiwa, water allocation has become a major source of ecological stress and community contention.

In many catchments, more water has been allocated than rivers or aquifers can sustainably provide, especially during dry periods. This has led to prolonged low flows, reduced sediment transport to the coast and diminished capacity to dilute contaminants. Braided river habitats have been lost, and thermal stress on aquatic species has increased.

The existing allocation model, based on a first-in, first-served approach, has entrenched historic inequities and discouraged efficient or adaptive use. Water is not priced or traded in most regions, offering little incentive to conserve it. Compliance monitoring is often inadequate, and cumulative catchment effects are not always accounted for in consent decisions. Allocation limits are based on historical flow data, which no longer reflect reality as climate change alters rainfall and river regimes.

The combined effect is a system that permits overuse and fails to adapt, threatening both environmental resilience and the sustainability of water resources for future generations.

The decline of freshwater quality and quantity has severely affected the ecosystems and biodiversity that depend on it. Because freshwater systems are interconnected, pressures in one part of a catchment cascade through the entire system.

River channelisation, dams and other engineering works have altered natural flow regimes, eroded habitats for native species such as kanakana (lamprey), tuna (longfin eel) and īnanga (whitebait), and blocked pathways for migrating fish species.

Invasive species such as trout and lagarosiphon (an invasive weed) have disrupted food webs and displaced native fish, while the loss of riparian vegetation has removed shade, stability and biodiversity corridors. Climate change adds further stress, altering rainfall patterns, prolonging droughts and increasing water temperatures.

The consequences are stark: an alarming number of New Zealand’s native freshwater fish species are now classed as at risk or threatened with extinction.