Nitrates Increase In Quarter Of West Coast Waterways - Report

Thursday, 7 August 2025, 5:01 pm
Article: Lois Williams - Local Democracy Reporter

Potentially harmful nitrate and phosphorous levels are increasing in a number of West Coast waterways with the intensification of dairy farming in the region. 

But in others, the levels are decreasing. Figures released in the Regional Council’s State of the Environment report this week reveal the good and bad news for the region’s water quality, biodiversity, air quality, land use and climate. 

Around 25 percent of West Coast waterways showed an increase in nitrate levels over the report period, from 2021 to 2024, mainly because of agricultural intensification. 

High nitrate levels in drinking water can damage aquatic life, and are linked to “blue baby” syndrome and cancer risks. 

But despite the rising levels, all the council’s monitoring sites were still well within national ecosystem health thresholds, the report found. 

At 17 percent of the sites monitored by the council’s science team, phosphorus levels were also on the rise.

“Eight sites were in the D band - below the national bottom line … indicating significant ecological risk,” the report said. High phosphorus levels in water can cause algal blooms toxic to humans and animals. 

On the plus side, nitrate levels decreased at 17 percent of the waterways and phosphorus levels had improved at 7 percent of the sites. 

The council’s Environmental Science Manager Shanti Morgan said the results generally reflected changes in farming practice: lower stocking rates and fertiliser use meant less nutrient run-off into streams and vice versa. 

Overall, 21 percent of all test sites showed declining trends. Riparian planting could help reduce runoff but was generally best for creating shade and helping stream clarity, Ms Morgan said. 

Suspended sediment levels – linked to farming, earthworks and mining - fell below the national bottom line at 27 percent of surface water sites, posing risks to aquatic life.

“We've had some C-band (poor) results - because of the recent long dry summers. ” Waterways showing the worst results for ecology, E coli, phosphorus and heat included Bradshaws Creek and Burkes Creek in Buller; Sawyer Creek and Pigeon Creek in Grey; Harris and Murray Creek in Hokitika and Duck Creek in Kokatahi. 

The council would prioritise its efforts to improve water quality based on the results in the report, Ms Morgan said.

Staff would take an educative approach, working with landowners and catchment groups where possible, and using tougher compliance measures as a last resort. 

The data contained in the report would directly inform the development of the new Land and Water Plan over the next three years, she said. 

In other findings, the report found climate trends showed the West Coast was experiencing highly variable rainfall and river flows, with both the wettest and driest seasons on record captured in the reporting period. 

Air quality monitoring showed Reefton had avoided breaching pollution standards until June 11 this winter - and would be monitored for another five years. New air quality monitoring work had begun in Greymouth and Hokitika. 

Land use figures showed 90% of the West Coast remained in a natural state, but continued expansion of exotic grasslands has reduced indigenous cover and wetlands over the past five years. 

Hazardous sites now numbered 533 on the council’s register, and staff were working with DOC and landowners to assess them. Biodiversity and biosecurity was being monitored at more than 300 sites up and down the Coast. 

Staff were working on early detection or control programmes for pest invaders including purple pampas grass - and deer which were now browsing a massive 30 percent of pasture in South Westland, the report found. 

Under the Resource Management Act, regional councils must monitor the state of the environment and report on the effectiveness of their plans and policies. 

Council chair Peter Haddock and chief executive Darryl Lew congratulated the science team on the 222-page report. 

“It’s a remarkable amount of work for this small team; other councils have been doing this for twenty or thirty years - we’re just starting,” Mr Lew said. 

The report was key to the council’s new efforts to involve land users in improving their catchments, he said. 

“We cannot get the improvements we need just by making rules and doing compliance,” Mr Lew said.

The state-of-the-environment report will be published on the council’s website and staff will launch a road show next month to share their findings with West Coast communities.

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