'Urban treasure' needs help

02:46, Feb 10 2014
Maitai Dam
MARKED CHANGE: Water from the Maitai Dam joins the South Branch of the Maitai River at this point, about 800 metres from the dam. The change in colour and riverbed quality is plain to see.

In the third part of a series looking at water quality issues in the Maitai River, Fish & Game regional manager Neil Deans tells Bill Moore that a combined effort could make a big difference.

The Maitai River is down but not out, a treasure that is "by no means stuffed", says Fish & Game Nelson-Marlborough regional manager Neil Deans.

A 20-year veteran of freshwater fisheries management and advocacy in the top of the south, Mr Deans says the river running through the city is an incredible asset.

"We're so fortunate to have a stream which by comparison to most has very good water quality, and is relatively natural and accessible, and can be used, or should be able to to be used, for people to go swimming and fishing and kayaking - you name it."

Mr Deans says the Maitai compares well with other New Zealand urban streams, and he classifies it as being "on the threshold of a problem". He says the establishment of the new group Friends of the Maitai is a positive step.

But the deterioration of the river is not news to Fish & Game, which has watched the decline in its trout population with disappointment and some frustration.


With an honours degree in science and a diploma in parks and recreation management, the articulate and informed Mr Deans is a formidable advocate for the region's rivers, and is quick to point out that what's good for trout is also good for eels and many other types of native fish.

"Trout fisheries are a good indicator of the health of waters, and one of the great treasures for Nelson has been that the Maitai historically was a very good and productive trout fishery, and was particularly noted for the abundance of the smaller fish, around 500 grams."

But in the past two decades, following the completion of the Maitai Dam in 1987, trout numbers have declined dramatically.

This might also be linked to the effects of exotic forestry on spawning tributaries like Sharland Creek, where Mr Deans has noted a lot of fine sediment, which isn't conducive to the growth of food and the survival of young fish, and can smother eggs.

Mr Deans has seen for himself the marked change in the river below the city water supply intake in the South Branch, and determined its excellent health above where the reservoir water is piped in to keep the river flowing above a minimum level - something Fish & Game fought for to protect trout.

"Any reservoir will affect water quality. By impounding water and then holding it in a reservoir, you get chemical changes to the water, and that's inevitable. You can see that simply in the discharge emerging from the Maitai reservoir as opposed to the South Branch, which is always clearer.

"The other issue is that whatever the better-quality water emerging either from the South Branch or from the reservoir, the better-quality water always goes to the city, and the worst-quality water always goes into the river."

In other words, when the river is at low flow, the water from the South Branch is better, and that's used for the city supply; when the river floods, the reservoir water is used.

There's a good economic reason for this, Mr Deans says, with the water treatment plant working better and more affordably with good-quality water feeding it.

So though there is more water in the river under low flow conditions - "they used to suck it almost dry" - the quality has declined.

"It's very hard to quantify how much effect that may have had on the whole biology of the river. I'd be very surprised if it didn't have some effect."

He also notes the tannin staining of the reservoir water but says, "it's still not an unhealthy river".

"I'm not suggesting for a moment that it's horribly polluted - it's not like that, and on balance we've still got a city that needs water. You can't expect no change. The question is, how pervasive is that change, and is it causing other unintentional changes?"

Then there are the tributaries. Mr Deans commends the forestry company that has responded to requests to clear out a culvert on Packers Creek to allow fish through, but says the result of harvesting trees and putting in roads might be the most significant cause of fish decline.

The Brook, on the other hand, suffers from a fully concreted lower section. It was once such an important spawning stream that Fish & Game closed it to fishing.

"That's kind of irrelevant now - fish can't get past the concrete section. It's just a thin ribbon of water. I suggested that [the Nelson City Council] create a slot on one side that carries the low flow [so fish could swim up it], but unfortunately, that got shouted down."

These are the sorts of things that could make a big difference to both trout and native fish, Mr Deans says. He also notes a seldom-used culvert across the Maitai that is often blocked by gravel, which he says the council is often tardy to clear.

He says the increasing cyanobacteria in the river is "a great concern", and that Nelson is lucky to have the Cawthron Institute's scientists on hand to try to solve the mystery of why it can suddenly change from safe to toxic.

There is also the sewage pollution that makes swimming in the lower Maitai a health risk - something Mr Deans says is difficult to trace the source of and fix but shouldn't be left to continue.

"I don't think it's good enough to be told, ‘Well, we've done these things and we haven't been able to isolate it - therefore, you cannot continue to swim, for example off the Collingwood St bridge', which 10 years ago kids did all the time."

He says this highlights an "inherent conflict of interest", because as a unitary authority - one of very few in New Zealand - the city council combines the functions of a regional council and a district council. It must provide water and treat sewage as a district council, but has resource management responsibilities as a regional council.

The lower Maitai is a very good case in point, Mr Deans says.

"Because there is no separation between the responsibilities of the regional council to improve the water quality and the district council to do the sewerage and provide water, the issue has fallen off the radar, and so you've had to have the establishment of a citizens' group to bring it back to public attention.

"It hasn't gone away - it just hasn't been addressed."

The council has been working on it, he says, "but it's all kind of disappeared into a black hole".

Mr Deans believes the council should talk with Friends of the Maitai, iwi, Fish & Game, the Department of Conservation, Forest & Bird and others to find out what their interests are, and what could be done differently to improve the river.

"The Maitai is well worthy of a bit more effort from all of us - it would make a really big difference."

He says the river is symbolic to Fish & Game, as an urban treasure that historically contained fish in abundance.

"We've created a pond out in the Waimea to try and encourage people to go fishing. The Maitai used to provide that for us for free, because it would naturally sustain that and people could go fishing on their bikes from their home. I'd love to see that returned."

FISH & GAME Is a statutory body funded entirely by licence holders, operating under Section 26B of the Conservation Act 1987 to represent anglers and hunters and provide coordination of the management, enhancement and maintenance of sport fish and game. This includes lobbying for appropriate environmental policies, developing and enhancing wetlands, providing advice, and advocating for clean water and environmentally sustainable farming practices. From a catchment of more than 100,000 people in the Nelson-Marlborough region, it sells between 5000 and 6000 fishing licences a year.