Diggers working in the Kaikorai Stream mouth the day before the discovery of hundreds of dead fish were working there lawfully.
Further, the Otago Regional Council’s own investigation into the matter was thorough, timely, and sound.
Two independent investigations into the significant fish kill in the estuary south of Dunedin in February were released by the council this week.
The reports cleared the council of misconduct.
However, the reports also linked the council contractor’s work to the fish kill and included a raft of recommendations for the council to improve its practices.
The circumstantial evidence was not enough to conclusively link the excavation of a channel in the sand bar to drain the estuary to the fish kill, investigators said.
But the discovery of dead smelt, flounder, giant bullies, trout and inanga at the edges of the troubled waterway at the Brighton Rd bridge one day after the work was done appears to have been avoidable.
Among the recommendations included in the reports is for the council to consult with Otago Fish & Game before similar work in the future.
Otago Fish & Game reported the fish kill on February 20.
The work to clear the channel was done on February 19.
It was done because on February 16 the council discovered the water level in the estuary was 100mm above its allowable limit and it had the potential to cause leachate from the Green Island Landfill to discharge into the estuary.
After the fish kill the regional council was determined to have responded quickly and it was able to rule out a toxic discharge in the stream.
The reports advised the council to monitor dissolved oxygen levels and water temperatures in the lagoon before any decision to open the estuary.
The council should arrange for mechanical openings to coincide with an incoming tide to avoid sudden drops in water levels and dissolved oxygen levels, the recommendations said.
It should enable mechanical openings to coincide with rainfall if possible.
It should open river mouths on windy days rather than hot, still days.
Also among the recommendations was for the council to aim for winter openings, and cooler conditions, which were environmentally better than opening river mouths during summer.
Council operations general manager Gavin Palmer said the engineering team would take the recommendations on board and incorporate them into future flood mitigation activities.
