Water Quality Monitoring
Monitoring freshwater quality helps us understand the health of Nelson’s rivers, streams, wetlands, and estuaries. Freshwater quality describes the physical, chemical, and biological condition of water, which influences ecosystem health, suitability for swimming and recreation, cultural and mahinga kai values, and the condition of downstream estuaries and coastal environments.
By regularly monitoring water quality, Council can:
- understand ecosystem health
- help assess progress toward Nelson Resource Management Plan Freshwater outcomes
- identify issues such as sediment, nutrients, bacteria, or low oxygen
- track trends over time
- inform management decisions and priorities
assess the effectiveness of restoration work - meet national requirements
- share clear, evidence‑based information with communities.
Water quality is influenced by both natural processes and land‑use activities across catchments, and monitoring provides the foundation for protecting and improving freshwater from the land to the sea (ki uta ki tai).
NCC Water Team gathering data at Roding River.
What We Monitor
Freshwater quality monitoring focuses on indicators that show how waterways are functioning and whether they are changing. Common measures include:
Water Clarity and Sediment
- Clarity and turbidity show how much sediment is suspended in the water
- High sediment reduces light, affects habitat, and can smother stream life
Bacteria (E. coli)
- Used as an indicator of contamination from human or animal sources
- Elevated levels can make water unsafe for recreation and stock drinking
Nutrients
- Nitrogen and phosphorus levels influence algal and plant growth
- Excess nutrients can degrade water quality and ecosystem health
Ecosystem Health
- Macroinvertebrates (MCI) - stream insects and invertebrates
- Aquatic plant growth
- These indicators reflect long‑term waterway condition
- Dissolved oxygen, pH, temperature
Sites are monitored every month for a range of tests, and biological monitoring is undertaken seasonally for freshwater macroinvertebrates, fish distribution and spawning. Samples and observations are collected following consistent methods.
Together, these measures help build a picture of freshwater health.
To see all the latest results for your river - Land, Air, Water Aotearoa (LAWA) - River Quality
Where and How Monitoring Occurs
Nelson City Council operates a network of 28 river ecology monitoring sites across five Freshwater Management Units (FMUs), including small streams within the Nelson-Stoke urban areas.
Click the links to see each site, what data is collected there and results.
The five FMUs in the Nelson region are:
NCC River Water Quality Monitoring sites in Nelson
For a more detail and interactive map - Land, Air, Water Aotearoa (LAWA) - River Quality
Swimming Water Quality
Nelson City Council monitors water quality at popular river and coastal swimming sites to help people make informed decisions about when and where it’s safe to swim. Monitoring is carried out during the summer swimming season, with results published on the LAWA “Can I Swim Here? website, where sites are given an overall recreation grade.
What We Monitor
Swimming water quality monitoring focuses on two key risks to human health:
- E. coli and enterococci – bacteria that indicate contamination from human or animal sources. Elevated levels can make water unsafe for swimming if ingested. These are monitored weekly at key river and coastal sites during summer.
- Cyanobacteria (toxic algae) – naturally occurring algae that can become harmful when river flows are low and temperatures are warm. Council monitors known hotspots and issues public health warnings when required.
What the Results Show
Most monitored beach sites and several river swimming holes in Nelson have Good to Fair long‑term recreation grades. Occasional exceedances are typically linked to rainfall events and high tides, which can wash contaminants into waterways or resuspend material along shorelines.
Some sites have consistently Poor grades due to ongoing upstream contamination. These locations are generally unsuitable for swimming, and people are advised not to enter the water.
When Not to Swim
Heavy rain can flush contaminants from urban and rural land into rivers and streams. As a precaution, avoid swimming for 2–3 days after heavy or prolonged rainfall, even at sites that usually have good water quality. Always check that the water is clean and clear before swimming.
Where to Find Information
During severe weather events, rāhui may be put in place to protect public health. Learn more about rāhui and what it means for river and coastal access.
NCC Water team at the Maitai River - looking for a good spot to place the sonde to gather data.
Using Monitoring Results
Freshwater quality data is used to:
- identify areas where water quality is improving or declining
- prioritise catchments for action
- inform land‑use and planning decisions
- support community and catchment groups
- meet regional and national freshwater requirements
The Nelson City Council Water Quality team gathers the data and sends through to LAWA host the results.
