River and stream health

Southland's water quality is a mixed bag. Some areas are good, but some are not. It's not all bad news, but there are key areas where improvements in water quality need to be made.

We run two programmes for rivers and streams - water quality monitoring and ecological-monitoring. When the results from the two programmes are combined, they indicate the overall health of a river or stream.

1. Water quality

We monitor water quality at 60 sites in 49 rivers and streams in Southland. Sites are visited monthly and samples/measurements are taken for both the physical properties (such as pH, temperature, and visual clarity), and the chemical characteristics (such as nutrients and dissolved oxygen). In addition, high flow sampling is carried out at key monitoring locations at the bottom of our major catchments to understand how much of a contaminant (including sediment and nutrients) is transported during high flows. Some of these key monitoring locations have continuous (every 10 - 15 min) records.

2. Ecological monitoring

Ecological monitoring involves monitoring the ecological health of our rivers annually at between 65 - 80 sites during late summer. In addition a subset of 30 sites is monitored monthly. The amount and type of slime algae on the bottom of the river bed (called benthic periphyton) the macroinvertebrates (e.g. insect larvae, worms and snails) and an assessment of habitat quality are some of the indicators recorded.

Scientists have found that Southland's water quality has been declining in intensively farmed lowland catchments throughout the region.

The results of monitoring and targeted investigations have identified the following key issues:

  • Rivers and streams in the developed areas of Southland generally have high levels of sediment, nitrogen and phosphorus. These levels are some of the highest in the country, as are nitrogen levels in groundwater.
  • Sediment and faecal bacteria levels across the region are also high from a national perspective.
  • Nitrogen levels in both groundwater and surface water are increasing over time.
  • The most sensitive parts of the catchments (the estuaries, lagoons and coastal lakes) are showing signs of stress. Ongoing measurements have found that the estuaries and lagoons in the region are rapidly deteriorating due to excess sediment and nutrients. This includes three of the region's main river catchments (Jacobs River Estuary, New River Estuary and Waiau Lagoon).

Monitoring fish in our waterways

Fish are an important part of a freshwater ecosystem. They sit at the top of the food chain and any changes in their food source, which can occur as a result of changes in water quality, can impact on fish species and populations.

Other activities, such as grazing of stream margins, drainage of wetland areas, and straightening of streams can also affect fish. For example, grazing of stream margins reduces the amount of shaded habitat which fish utilise to shelter from high water temperatures.

A diverse range of fish species live within Southland's freshwater bodies, from introduced sports fish such as rainbow and brown trout, to native eels, bullies and whitebait.

Since 2007/2008 Environment Southland has been undertaking fish surveys. They are captured via electric fishing in an enclosed part of a stream or river, then counted, measured, identified and released.

Through fish monitoring we aim to:

  • Record an inventory of fish species/populations in selected streams on an annual basis
  • Identify changes in fish numbers and species diversity due to impacts of variable habitat availability and quality
  • Add to the water quality testing and bio-monitoring work carried out by Environment Southland to provide a greater indication of overall catchment health and longer term issues
  • Collect important data for setting environmental (or minimum) flows, as we need to ensure adequate habitat is provided for fish and other aquatic life

Future monitoring – building on our knowledge base

We are currently investing in a comprehensive science programme to build upon existing monitoring programmes. This will allow us to better understand Southland's waterways and how they respond to pressures from different land uses.

→ Find out more about the Southland Science Programme​

Page reviewed: 18 Feb 2019 12:45pm