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  Environment » Natural Resources » Water » Rivers » How healthy are our rivers? » Stream and river life

Stream and river life

The streams and rivers of the Waikato region are home to 22 types of native fish, as well as freshwater crayfish (koura), shrimps, and invertebrates. Our aquatic plants and animals are under threat from habitat loss and introduced pests.

Photograph of a female redfin bully

On this page: Fish, Stream invertebrates, Aquatic plants, Threats to life in our rivers, What you can do to help, Find out more


Over the last hundred years, native fish populations in the Waikato region have decreased dramatically, mainly because of changes to their habitat. One native fish, the grayling, has become extinct.

Many of our native fish travel between freshwater and the sea as part of their life cycle. Structures such as over-hanging culverts and dams can block fish access. Land drainage, flood protection schemes, and introduced pest fish can also affect our native fish.

The table below lists native freshwater fish found in the Waikato region.

Table 1: Native freshwater fish of the Waikato region

Common name (Maori name)Scientific name
Yellow-eyed mullet (Aua) Aldrichetta forsteri
Shortfin eel (Hao) Anguilla australis
Longfin eel (Kuwharuwharu) Anguilla dieffenbachii
Australian longfin eel Anguilla reinhardtii
Lamprey (Pirahau) Geotria australis
Torrentfish (Papamoko) Cheimarrichthys fosteri
Giant kokopu (Kokopu) Galaxias argenteus
Koaro Galaxias brevipinnis
Dwarf galaxias Galaxias divergens
Banded kokopu (Para) Galaxias fasciatus
Inanga Galaxias maculatus
Short-jawed kokopu Galaxias postvectis
Black mudfish Neochanna diversus
Giant bully Gobiomorphus gobiodes
Upland bully Gobiomorphus breviceps
Common bully (Pako) Gobiomorphus cotidianus
Bluegill bully Gobiomorphus hubbsi
Redfin bully Gobiomorphus huttoni
Cran’s bully Gobiomorphus basalis
Grey mullet Mugil cephalus
Common smelt (Ngaoire) Retropinna retropinna
Black flounder (Patiki) Rhombosolea retiaria


There are 14 species of introduced fish found in the Waikato region. Some, such as the sailfin molly and guppy, are originally from the tropics and can only survive in areas of geothermally heated water.

Other introduced species have spread into the region’s rivers, such as rudd, koi carp and catfish, and some are a threat to our native species. The table below lists introduced freshwater fish found in the Waikato region. Find out more about aquatic pests.


Table 2: Introduced freshwater fish found in the Waikato region

Common nameScientific name
Catfish Ameiurus nebulosus
Goldfish Carassius auratus
Grass carp Ctenopharyngodon idella
Koi carp Cyprinus carpio
Gambusia or mosquito fish Gambusia affinis
Rainbow trout Onchorhycchus mykiss
Perch Perca fluviatilis
Sailfin molly Poecilia latipinna
Guppy Poecilia reticulata
Brown trout Salmo trutta
Brook char Salvelinus fontinalis
Rudd Scardinius erythropthalmus
Tench Tinca tinca
Swordtail Xiphophorus helleri


Stream invertebrates

Photograph of a feather-winged beetle

Invertebrates are animals without backbones. They include all insects, snails, crustaceans and worms. The larvae of many insects that spend their adult life out of the water, such as mayflies and beetles, start their lives in streams and rivers.

Waikato Regional Council uses the number and type of invertebrate species found in streams to assess stream health, for example:

  • mayfly, stonefly and caddisfly larvae are found in streams with high quality habitat, for example, in the headwaters of catchments covered in forest
  • snails and worms are more common in degraded streams and rivers especially those in the lower catchments where there is urban or agricultural development.

Nearly half of the Waikato Regional Council monitoring sites in developed catchments are either moderately or severely degraded. These streams are often in:

  • urban areas where streams can contain heavy metals and more sediment
  • agricultural catchments where vegetation clearance and land development has caused increased water temperatures and greater accumulation of silt on the streambeds.

Aquatic plants

The aquatic plant communities in rivers and streams are made up of algae, mosses, and submerged plants with leaves. Before European settlement, most waterways were very shady because of the native forest surrounding them and supported a range of native aquatic plant species. Now most of our streams and rivers are in developed catchments and are dominated by introduced plants such as the oxygen weed, Egeria.

These introduced plants can provide instream cover for other plants and animals, but when stream flows are low during summer they can reduce the dissolved oxygen in lowland agricultural streams.

Threats to life in our rivers

Before European settlement, New Zealand's rivers and streams flowed from the mountains to the coast through native forest and grassland communities. These forests and high altitude grasslands kept our smaller rivers and streams cool and shady. The clearing of this vegetation has made stream temperatures more variable, and less suitable for many of our native aquatic animals and plants.

In addition to habitat loss through land clearance, our aquatic plants and animals have also been affected by other aspects of development including:

  • barriers to fish passage
  • reduced water quality
  • changes to flow regimes
  • habitat loss (due to drainage and changes in land use).

Some introduced species become pests that compete with or eat our native fish. Find out more about troublesome fish in the Waikato River.

Waikato Regional Council has been working with the Department of Conservation to stop the spread of aquatic pests such as koi carp.

What you can do to help

  • Never release exotic fish into waterbodies (not even into farm or garden ponds).
  • Install fish passes on or remove structures that block fish access.
  • Install culverts properly with their bottoms below the natural stream bed level.
  • Fence and plant riparian margins, especially in lowland areas.
  • Avoid excessive drainage, stopbanking and unnecessary dams.
  • Check boats and fishing gear carefully to remove any weed, juvenile fish or eggs.

Find out more

Find out about the birds, fish and plants that live in our riverine lakes.

Find out about the plants and animals that live in Lake Taupo.

Find out about wetland plants and animals in our region.

Check out our publications about freshwater habitats.

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