Publications: Research reports and publications

What is a healthy river?

Cawthron Report No. 3035. Prepared for Cawthron Foundation

Young R, Wagenhoff A, Holmes R, Newton M, Clapcott J 2018. What is a healthy river?.
Prepared for Cawthron Foundation. Cawthron Report No. 3035. 45 pages



New Zealand’s rivers provide habitat for a wide range of species. People cherish rivers for the cultural, social and economic values that water bodies provide. The public is anxious about the plight of our rivers and streams, believing the ecosystem health of these waterways must be diagnosed and upheld just as we care for our own health. While most of us agree that ecosystem health is a worthy goal, there is confusion about just what the term means, and whether we are measuring it correctly. To promote more informed debate on the topic, this report presents a review of the science of ecosystem health in rivers. It describes how indicators of river health are currently used in freshwater policy and management in New Zealand. We look at overseas approaches to the development and use of freshwater indicators and how these might apply in New Zealand. Finally, we identify some key requirements for improved river health assessment and management in New Zealand.

People intuitively recognise the value of the ecosystem health concept, although they may describe it in different ways. This diversity of views suggests that a range of interested groups should join to collectively decide society’s goals for ecosystems, and how these can be achieved. In science, there is some overlap between ecosystem health with the concepts of ecological integrity, ecosystem services and life-supporting capacity. The law, via the National Policy Statement for Freshwater Management, defines ecosystem health in a narrower way than its use in the scientific literature, which focusses on both ecological and human use values. Human use values are addressed separately in the National Policy Statement for Freshwater Management.

Ideally, river health indicators give an early warning of impending concerns, show whether conditions meet acceptable limits and help diagnose the causes of poor health. However, a single indicator will never fulfil all these purposes. A complete assessment of river health measures physical structure, water flow, biological community composition, and ecosystem processes and functioning, along with the water quality parameters which have dominated river assessments in the past. The scale of indicator measurement is important in both space and time, since some factors influence river health locally or over specific periods while others can have widespread effects. Interpretation of indicator results often requires knowledge of expected reference condition (the river’s benchmarked or desired state), so assessments can take account of natural differences in climate, geology and species distributions. Indicators can provide a picture of current river health and show if conditions are improving or getting worse. Reporting of river health needs to be as simple as possible, while capturing the key ecological features described above. Indices that combine information from all these elements show some promise, but users must ensure that no information is lost in the mix and results remain intuitive and easy to understand. To this end, ‘report cards’ are becoming an increasingly popular approach to presenting information on the health of rivers.

Our review of river ecosystem health monitoring and management approaches in Europe, the United States, Australia and Canada identified several crucial elements that are relevant to New Zealand. These are worth considering in future efforts to improve our river health assessment and management programmes. Strong national policy drivers for the management and monitoring of river ecosystem health are critical, with stakeholder participation in planning and implementation. Policy should include clearly stated, overarching goals for river ecosystem health as well as measurable, numeric objectives. Managers need a range of biological measures (metrics) as well as measures of pollutants, water quality, flow regime and habitat condition to diagnose issues and guide effective management interventions. Policy and management actions also need to consider the cumulative effects of multiple pressures (stressors). Standardisation of field and laboratory protocols across water management authorities is required to capitalise on the value of large monitoring datasets. Finally, effective communication of the results of river health assessment to politicians and the wider public is important. Some of these critical elements are already in place in New Zealand, but for others more effort is required.

To improve current practice, we need clear recognition that a healthy river requires more than just good water quality. Ideally, some indicators of river health should link clearly to freshwater values expected by the community. Further development and use of kaupapa Māori frameworks for assessing river condition may help recognise and incorporate the interconnections between ecological and human use values. Report cards and on-line reporting of river health information give an opportunity for communities to better understand if their objectives for river health are being met and what can be done if they aren’t. There are also gains to be made through empowering citizens by giving them the tools to collect information and contribute to a better understanding of river health in New Zealand. New Zealand has the opportunity to develop and embrace new technologies that will provide better information on river health and help ensure that our rivers maintain or reach the ecological structure and functioning that is needed to support society’s uses and values of fresh water.