The death of hundreds of fish in a Dunedin stream recently is symptomatic of a failure by regional councils across the country to properly manage the country's waterways, says Fish and Game.
Dead smelt, flounder, bullies, trout and inanga (whitebait) were found littering the shoreline around the Brighton Road bridge at Kaikorai stream over the weekend, sparking an investigation by the Otago Regional Council (ORC).
A council pollution team visited the site and took water samples to see if there was any pollution from an upstream source that could have been responsible for the deaths, with the results still pending.
Earlier this week Otago Regional Council's regulatory general manager Richard Saunders said the most likely scenario was warm temperatures and reduced dissolved oxygen in the water "exacerbated underlying water quality issues in the stream, leading to the fish deaths".
He said it was also possible flood protection work by the council was a contributing factor.
"Opening the coastal mouth is something ORC does regularly as a flood protection measure, and it's essential to avoiding leachate from the Green Island landfill entering the stream," he said.
"While opening the coastal mouth has not been associated with fish kills in the past, it is possible that it was an exacerbating factor in this fish kill event – that's something we hope to understand from our investigation."
But on Friday, chair of the Fish and Game Council Ray Grubb said it was "galling" that the fish deaths were possibly caused by the council's own actions, and says the incident is "symptomatic of regional councils across the country failing to manage the environmental impacts of land-use on our waterways".
"This environmental tragedy wasn't an isolated incident, and it isn't limited to my home patch, Otago," Grubb said.
He said estuaries are vitally important ecosystems that support a large diversity of species and are breeding and feeding grounds for fish and birdlife.
However, he said many of these ecosystems are now close to flipping - "reaching a point where they are so polluted that they can no longer sustain life" - and laid the blame with regional councils.
"Regional councils are supposed to be responsible for sustainably managing natural resources and implementing the rules around water quality and quantity. In many cases the rules are inadequate, but even when they are sufficient regional councils fail to enforce them, instead focusing more on regional development and economic growth, and ignoring the environmental costs."
Saunders told Newshub on Friday the council was still waiting for the results of the water samples taken upstream, which would indicate whether any upstream pollution may have played a part in the incident.
"The Kaikorai stream is an urban stream, and we know that waterways in towns and cities suffer some of the worst water quality impacts," he said.
"The Government’s National Policy Statement for Freshwater Management (NPSFM), introduced last year, requires that water quality degradation is reversed and actions are identified to improve the health of water bodies that do not meet NPSFM bottom lines.
"ORC is undertaking a full review of our water plan to give effect to this policy across Otago – including in urban streams such as the Kaikorai."
General manager of operations Gavin Palmer said whether the council's river mouth opening activity had anything to do with the fish deaths remains under investigation.
"We would look to make changes to how we conduct the activity if it is found to be a factor," he said.