Dead fish, including smelt, flounder, giant bullies, trout and inanga, littered the edges of the Kaikorai Stream and estuary at the Brighton Rd bridge.
ORC regulatory general manager Richard Saunders said yesterday it would investigate the fish deaths and whether there was any pollution from an upstream source.
He said the opening of the coastal mouth, which occurred over the weekend, could also have contributed to their deaths.
The council’s engineering team opened the coastal mouth at the Kaikorai estuary regularly when the stream reached a point at which it could cause water to flood and backfill into the Green Island landfill leachate fields, Mr Saunders said.
The council’s pollution team attended the site of the fish kill at Kaikorai Stream on Saturday, and took water samples for testing.
The stream had underlying water quality issues.
"The most likely scenario in this case is that warm temperatures and reduced dissolved oxygen in the water exacerbated underlying water quality issues in the stream, leading to the fish deaths," Mr Saunders said.
“Opening the coastal mouth is something [the council] does regularly as a flood protection measure, and it’s essential to avoiding leachate from the Green Island landfill entering the stream."
Opening the coastal mouth had not been associated with fish kills in the past, but it was possible that it was an aggravating factor in this fish kill event, he said.
The fish kill highlighted that water quality was everyone’s responsibility, in urban contexts as well as rural, he said.
Urban waterways had some of the most degraded water quality in New Zealand, he said.
"It’s crucial that people are conscientious about what’s going into the streams and rivers in their backyards, and avoid draining anything that might negatively impact the environment," he said.
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Saunders is right, high temps and low dissolved oxygen is most probable. Sadly Fish&Game lept at the chance to blame farming at any opportunity. They need to turn the mirror on themselves, a recent region-wide study found 80% of feacal bacteria in rivers is from their ducks not farmers! They wont admit that publicly however
According to yesterday's article Otago Fish & Game chief executive Ian Hadland did not mention farming once in connection with this incident. Do you know otherwise?
I was interested in the study you mentioned so did a quick Google and found that what you state is a little misleading. The Southland based study found that 80% of samples taken were found to contain bird poo. This is not surprising due to many wild birds living in close proximity to water. However the study also found that 50% of the samples contained livestock faecal matter and a small percentage even contained human waste.
"Environment Southland science manager and report author Dr Elaine Moriarty said the risk of becoming sick after swimming in a river that contains bird pollution is low, while the risk of swimming in a river with even a small amount of pollution from human or ruminant sources is very high as the diseases this pollution carries are more readily transmitted to humans."