Water quality data reveals a 'very mixed bag' for Canterbury rivers

Monday, 28 September 2020

A Selwyn Huts resident says pollution has 'Chernobylised' the Selwyn River (Video first published December 2019).

New river water quality trends reveal a “very mixed bag” for Canterbury waterways.

It reflects the national findings from Land Air Water Aotearoa’s (Lawa) latest update to 10 years of water quality data, released Sunday to mark World Rivers Day.

It found urban waterways generally had the worst water quality, followed by those flowing through pastureland, while those in native forest had the best.

The water at Coes Ford, on the Selwyn River, is in the worst 25 per cent in the country for total nitrogen levels.

Lawa’s summary for Canterbury said the region had been experiencing declines in water quality in recent years, with lowland streams having the poorest quality.

The monitoring looked at several water quality indicators such as levels of E Coli (a bacteria that indicates fecal contamination), nitrogen, and phosphate, and the macroinvertibrate community index (MCI), which looks at whether insects that indicate river health are at the site or not.

* Where we used to swim: The turning point for Canterbury's Selwyn River

Although the water quality in the Waimakariri River is among the country’s best by several indicators, it is worsening.

One expert said it was hard to find a Canterbury river where at least one indicator was not degrading, but improving quality was a long-term game and people need to keep their eye on the ball.

For the Avon River in central Christchurch, the river was in the worst 25 per cent of those monitored nationally for E. Coli and total nitrogen and was graded D for MCI (the lowest available), but all three of those indicators were improving.

The Heathcote River at Bowenvale Ave was also in the country’s worst 25 per cent but showing an improving trend for E. Coli, phosphorous and nitrogen.

The Avon River scores poorly by many indicators, like many urban rivers in New Zealand.

The Waimakariri River at the old highway bridge was in the country's best 25 per cent for nitrogen and total phosphorous, and the best 50 per cent for E. Coli, but was worsening in all three measures. It scored a C for MCI.

At Coes Ford on the Selwyn River, the water quality was in the worst 50 per cent for E. Coli and worst 25 per cent for nitrogen, and was degrading in both indicators. Its MCI was graded C and was also degrading.

Environment Canterbury (ECan) chief scientist Tim Davie said there was a strong link between intensive land use and poor water quality.

A section of the Heathcote River is also in the country’s worst 25 per cent, but showing an improving trend for E. Coli, phosphorous and nitrogen.

“The most intensive land use, with the greatest modification from natural, is in the urban areas and this is where we consistently see the worst water quality.

“The second-most intensive land use is in our pastoral farming areas which make up large parts of Canterbury; these are not as poor water quality as urban areas but do show a large decline in water quality from our native vegetation catchments.”

ECan chair Jenny Hughey said water quality was a challenge the regional council had been addressing for several years. In rural zones, there were auditable farm environmental plans, nutrient limits and rules to keep stock out of waterways.

Restoration work was being done by water zone committees, farmers, and various community groups, Hughey said.

Jenny Webster-Brown, the former director of the Waterways Centre for Freshwater Management, said the Canterbury results were a “very mixed bag” and for every river that was degrading, one was improving.

But it was hard to find a Canterbury river where at least one indicator was not degrading, and even those that were in good shape, like the Waimakariri, were showing some signs of degredation, Webster-Brown said.

In some rivers, the MCI was getting worse even though all other indicators were improving.

The MCI provided a cumulative look at river health, so if that was deteriorating while other indicators improved, there was something affecting the river that was not being taken into account.

Webster-Brown said there was a feeling that if we did some riparian planting the whole thing would come right but that was not the case, and a concerted effort to improve water quality was needed.

She said improving water quality was a long-term game and these results were a wake up call that we could not take our eyes off the ball.

The Government recently proposed a nationwide freshwater plan aiming to protect and restore waterways from contamination.

It would try to improve water quality for rivers, lakes and wetlands within five years and fix them within a generation.