Activities that affect freshwater species and ecosystems

Clearing native forests and draining wetlands

When settlers arrived in Aotearoa New Zealand they cleared areas of forests and drained wetlands to make way for farming. This led to a loss of habitats and a decline in the number of species. Today, only 10 per cent of our original wetlands remain.

Over the years, we have continued converting land in our catchments to suit our needs. This has reduced the water quality and put pressure on many freshwater habitats and species.

Some water catchments have been more affected than others. For example, lakes and rivers with upstream catchments in urban and pastoral land are in worse condition than those with upstream catchments in areas with native vegetation.

Changing waterways from their natural form

Many native fish need to migrate up and downstream and to and from the sea to complete their life cycles.

Structures like dams, weirs and tide gates in streams and rivers can make this difficult. This can lead to reduced fish populations and affect natural stream processes.

Fishing

Fishing can also reduce freshwater fish populations and affect habitats.

For example fishing and habitat loss, and barriers to fish migration have reduced the number of large longfin eels nationwide.

Introduced species

Introduced species compete with native species for food and space. They also damage existing habitats.

There are now 21 non-native freshwater species in New Zealand. Those of greatest concern include koi carp, perch, and bullhead catfish. Introduced fish accounted for more than 80 per cent of our fish species at 925 river sites from 1999-2018.

Our waters are now home to 41 introduced plant and algae species. Many introduced plants form tall dense weed beds and spread quickly. They can take the place of native freshwater species and make the habitat unsuitable for native fish and invertebrates (eg native snails).

Find out more in Our freshwater 2020 environmental report

Conservation status of indigenous freshwater species

Figure 1. Two bar graphs.
The majority of freshwater birds and fish are threatened with or at risk of extinction. Many freshwater invertebrates are currently not under threat.

Image: Department of Conservation

Figure 1. Two bar graphs.
The majority of freshwater birds and fish are threatened with or at risk of extinction. Many freshwater invertebrates are currently not under threat.

Image: Department of Conservation