Samples collected over the past 10 years from river sites around the country show that water quality is poorest in urban waterways, while a large percentage of rivers in catchments dominated by pasture are under pressure.
Not surprisingly, the best water quality is found at sites surrounded by native bush.
The samples, currently taken from 1500 river sites, about 400 more than six years ago, have been analysed by the Cawthron Institute.
The institute’s freshwater ecologist Dr Roger Young, who led the analysis, says looking across four key indicators of water quality – E. coli, dissolved reactive phosphorus (DRP), macroinvertebrate community index (MCI) and ammonia toxicity – it is clear that land cover, and by implication land use, has a significant effect on the health of NZ waterways.
“For the national level analysis, we focused on the state of our rivers and streams and looked at how this compares for different land cover types, and how it has changed over time,” Young said.
“We found water quality was best in our native vegetation streams and worst in our urban waterways.
“Unfortunately, we found the overall state of E. coli, MCI, ammonia toxicity, and DRP has not improved over the past 10 years and that more work and time is needed for the benefits of restoration efforts to become apparent.”
Hawke’s Bay Regional Council chief executive and Ministry for the Environment (MfE) Freshwater Implementation Group member James Palmer says the data adds weight to the need for greater action on the ground to improve water quality.
“The challenges at our urban, pastoral and non-native forest monitoring sites show the stress rivers are under, following more than 150 years of population growth and changes to land use,” he said.
“While the Government’s Essential Freshwater package moves us in the right direction, to see meaningful progress in water quality is going to take time and will require a joined-up response from communities, industry, iwi, councils and central government.”
Palmer says the data underscores the challenge ahead and the amount of time it takes to make a difference.
He says the picture the data paints is that freshwater quality has not gotten much worse during the past 10 years, but it has not got much better either.
It will take decades for real improvement to show up.
Environment Canterbury chief scientist and LAWA river water quality lead Dr Tim Davie says through improved regional council monitoring networks and science programmes the sector is learning more about where the pressures are.
“Since 2015, the number of river and stream sites regularly monitored by the regional sector and reported on the LAWA website has increased by more than a third,” Davie said.
“This represents significant investment and a commitment to better understanding our freshwater quality and the interventions that can help.
“Interventions to improve river health include preventing sediment and nutrients entering waterways, upgrading infrastructure, using water sensitive urban design, restoring stream habitats and ensuring appropriate flows.”
He says the latest data shows that everyone has a part to play in improving water quality.
“We all need to up our game. There’s not an urban/rural divide. It’s an issue for all New Zealanders,” he said.