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Rivers and streams

Native bush streams

Example of a native bush stream

Cascade Stream is an example of a hard-bottomed native bush stream. It flows through the Waitakere Ranges, an area of protected native forest that provides a beautiful natural environment. The ARC has been monitoring its water quality since 1986.

What is a native bush stream?

A native bush stream flows through a catchment area of native forest for most, or all, of its length. Just under one third of the land (about 135,000 hectares) in the Auckland region is covered by native bush and scrub.
The health of a native bush stream and the types of life (ecology) in and around it is influenced by the following factors.

Riparian vegetation

Large numbers of native trees and shrubs grow alongside a native bush stream and provide plenty of shade throughout the year. They protect the water from direct sunlight and keep it at a cool temperature. They also provide a variety of habitats for different bird, insect, invertebrate, fish, and amphibian life.

Leaves and other organic matter from decaying forest vegetation wash into the stream and provide an important food source for the organisms living in the stream. Larger pieces of woody debris in the stream provide a variety of habitats to suit different organisms.

Land use in the surrounding catchment

At least 95% of the land in the catchment area of a native bush stream is covered by mature or regenerating native forest. There is very little, or no, urban development and there may be a very small amount of exotic forest.

The native bush catchment means the water is almost free of bacterial contamination and other contaminants such as heavy metals from domestic and industrial pollution. There are very few nutrients (such as nitrogen and phosphorus) washing into the water to feed plant and algal growth, and very little sediment.

All of these factors mean that the water quality, the physical environment, and the fish, invertebrates, insects, amphibians, and birds living in and around native bush streams remain very close to their natural state, except for the effects of introduced predators such as possums and rats.

Because of this, we can use a native bush stream as a benchmark or reference site against which we can compare other types of stream (rural, urban and forestry streams). Cascade Stream is an excellent reference site for the Auckland region.

Typical water quality of a native bush stream

The lack of urban land cover means that native bush streams have the best water quality and the lowest water temperatures amongst the four types of stream (urban, rural, forestry, and native bush) found in the Auckland region.
In particular, native bush streams have:

  • high levels of dissolved oxygen
  • cool water temperatures of around 13 to 14° C
  • lower levels of suspended solids and turbidity
  • very low levels of nitrogen and phosphorus
  • very low levels of faecal bacteria.

Typical invertebrate ecology of a native bush stream

Native bush streams have the highest varieties of invertebrates amongst the four types of stream in the Auckland region. More than 30 types of taxa are usually found. The regional average is 18.

Many of the sensitive mayflies, stoneflies and caddisflies require a high quality stream environment with high levels of dissolved oxygen, cool water, permanently flowing water, and a stony bottom. Hard-bottomed native bush streams provide this type of environment so more than half of all the invertebrates collected in native bush streams consist of these sensitive taxa.

The two most important factors that affect the ecology of any stream appear to be the water quality and the water temperature.

What is being monitored?

 The Freshwater Ecology Programme is monitoring the biological health and the physical condition of some streams in the Auckland Region.

The Rivers & Streams Water Quality Programme is monitoring the water quality.

When the results from both programmes are combined, they give a good indication of the overall health of a stream and its physical, chemical, and biological condition.

Technical Publications

The ARC has a number of technical publications relating to this subject. Follow this link to see the full list of ARC techncial publications.