New Zealand's distinctive combinations of climate, geology and landforms gives rise to great diversity in the country's freshwater ecosystems.

The tectonic uplift that created our mountains also helped form the patterns of braided rivers in the eastern South Island. Glaciation events and earthquakes have driven the formation of many lakes, tarns and wetlands.

More than 425,000 km of mapped rivers and streams flow across Aotearoa New Zealand. These include 70 major river catchments – 40 in the South Island and 30 in the North Island.

There are about 50,000 lakes, as well as geothermal and cold-water springs, karst systems.

Water also flows underground through 200 identified aquifers.

703 (88%) indigenous freshwater species are endemic. This highlights the amount of speciation that has occurred through the country's 80 million years of geographic isolation.

State and trends

The factors that disrupt harvesting customary resources, and prevent iwi from fulfilling the obligations of kaitiakitanga are:

• the decline in the quantity, quality and mauri of fresh water since human arrival
• habitat and species loss
• poor water flows
• poor ecosystem conditions

More than a third of monitored lakes are considered to be in poor ecological health or lacking submerged plants.

Of the 976 freshwater species assessed:

• 14% are ranked as 'Threatened'
• 17% are 'At Risk'
• 44% of indigenous freshwater fish are threatened with extinction.

What we don't know

Over a quarter of freshwater species (218 species; 22%) assessed under the NZTCS are assessed as being 'Data Deficient'.

The taxonomy of many groups is not well defined, and knowledge gaps in the distribution, abundance and population dynamics of many species make it difficult to assess their conservation status.

For example, freshwater invertebrates (such as kōura/freshwater crayfish, kākahi/freshwater mussels, insects) are important to a freshwater ecosystem, but their conservation is hampered by a lack of knowledge.

Freshwater biodiversity pressures

Pressures in freshwater ecosystems are largely the consequences of:

• human activities (directly) such as land development, water extraction, damming, harvesting
• productive activities (indirectly) such as farming and industry
• invasive species
• climate change

These pressures degrade the quality and quantity of both surface and ground water. They can weaken ecosystems, and lead to the loss of biodiversity values.

The major pressures on freshwater life are the cumulative impacts from poor water quality, altered river flows, physical barriers, habitat modification and invasive species. 

The full consequences of climate change are not fully understood. However, they are expected to worsen the range of impacts on freshwater species.