Horne Creek fish deaths remain unexplained

The reason for the sudden deaths of up to 150 fish in a Queenstown stream may remain unknown, as results of tests done on water taken from the site have not identified any obvious toxin.

What killed the fish? ORC remain none-the-wiser.

Members of the public alerted local authorities to masses of fish floating dead in Horne Creek, which empties out into Lake Whakatipu at Queenstown Bay.

Otago Regional Council staff initially visited the site over two days, taking water samples from the creek and retrieving the dead fish, which were mostly trout but included one native galaxiid.

After an extended wait, results from tests done on the water samples are in from a Christchurch laboratory, and they are "inconclusive". 

ORC compliance manager Tami Sargeant says her team had been hopeful the test results would help them establish what had happened along the stream.

“It’s unfortunate, the samples are inconclusive and don’t help us to narrow down any offending substance.”

If it was a pollutant that killed the fish, it's possible it may have only been in the waterway for a short time and wasn’t there when the water samples were taken, she says.

Reports of the dead fish emerged on Facebook on April 30, but it was a day later, May 1, before the regional council's pollution watchdogs first visited the stream.

In an initial media statement, the ORC said autopsies of some of the fish were underway, in addition to the water testing.

Later, the ORC said tests on the dead fish had not been done.

Mrs Sargeant says the council has received no additional information from any members of the public to help shed further light on the possible pollutant.

It's not the first time something fishy has happened at Horne Creek - in August it flowed green.

Anyone with any information on what may have been discharged into the creek, killing the fish, can still come forward on the ORC’s Pollution Hotline on 0800 800 033, she says.

The stream at the point where the dead fish were located passes through a mix of rural and industrial land; downstream, it passes through residential and commercial areas.

There's right and wrong ways of disposing of potential pollutants, and the ORC is keen to remind people chucking any old liquid down a drain or into a gutter isn't as simple as out-of-sight, out-of-mind.

"In urban environments, rainwater runs into gutters and is collected in stormwater pipes, which can feed directly into the nearest waterway. Watercress, eels and other fish can die or become contaminated by toxins washed in via stormwater."

The ORC has an industry guide, Only Drain Rain, that outlines how to dispose of potential pollutants correctly.

In August, members of the public also raised the alarm after a section of Horne Creek turned a fluorescent shade of green and a hunt began for the source of the pollutant.