Water takes toll on native species

Most of New Zealand’s native freshwater species are at risk of extinction as water quality faces ‘‘serious pressures’’, a government report says.

Threats to native species were one concerning aspect amid an overall decline in freshwater quality, determined in a joint report by the Ministry for the Environment and Statistics New Zealand.

The document added to mounting evidence that freshwater quality will get worse unless fundamental changes are made.

The report, titled Our Freshwater Environment 2017, found nearly three-quarters of native freshwater fish species were threatened by or at risk of extinction, as well as a third of native freshwater invertebrates and a third of native freshwater plants.

The study – part of the State Of The Environment reporting series – measured water quality, quantity, biodiversity and cultural health. It found problems in all categories.

Nitrogen levels were worsening at more than half of the measured sites, according to the report. Nitrogen levels were worst at urban sites but were falling significantly in pastoral areas.

This decline in pastoral areas coincided with an increase intensive agriculture. Nitrogen leaching from agriculture had increased by 29 per cent since 1990, it said. The main source was livestock urine.

Urban waterways had the worst overall quality, degraded by stormwater and wastewater. About a quarter of wastewater assets are more than 50 years old.

‘‘Urban water is the most polluted but the trends are worse in pastoral areas,’’ Secretary for the Environment Vicky Robertson said. ‘‘Very high levels of nitrogen can be a problem as they can make water toxic for species and unsafe for drinking.

‘‘We aren’t seeing this playing out yet, but as nitrogen levels are trending the wrong way, this is something we need to address.’’

While much of the water quality debate had been on swimmability, the report highlighted serious health issues for native species. They faced big threats, including degraded habitat from contaminated water, altered flows and introduced predators.

‘‘Many of our species are found nowhere else in the world so it is even more crucial we don’t lose any under our watch.’’

The report said 72 per cent of native freshwater fish were threatened by or at risk of extinction, including four whitebait species, lamprey and longfin eels. The once-common grayling is already extinct.

A third of native freshwater invertebrates were in the same category; 10 per cent were deemed to be at thenationally critical level. ‘‘A lot of our native species are endemic so if we lose them, they’re gone forever,’’ Robertson said.

The report’s findings were welcomed by scientists and environment and industry groups, however gaps in the data proved contentious. Forest & Bird said the report largely drew from data that was more than three years old.

‘‘The report doesn’t show us upto-date trends, which we’d hoped for and which we think the country needs,’’ said freshwater advocate Annabeth Cohen.

Irrigation NZ said the report was based on ‘‘limited data’’, which made it hard to track progress. ‘‘We know that where farmers and growers are focusing their efforts, they are making a difference. This report does reflect this ... but it is very constrained due to incomplete or inconsistent data,’’ chief executive Andrew Curtis added.

"A lot of our native species are endemic, so if we lose them, they're gone forever." Secretary for the Environment Vicky Robertson