ORC Compliance Manager Tami Sargeant says the test analysis results have just been returned from the Christchurch laboratory.

“We were hoping the tests would help us establish what happened along the stream,” she says.

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

Mrs Sargeant says the problem may have been that the pollutant which might have caused the fish deaths may have only been in the waterway for a short time and wasn’t in the stream when the water samples were taken.

That meant if any pollutant discharge had occurred, it was likely no longer present in the stream, she says.

No information has yet been received from the public, who can still come forward on the ORC’s Pollution Hotline on 0800 800 033.

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

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.

ORC have an industry guide, Only Drain Rain, which outlines how to dispose of potential pollutants correctly.

Mrs Sargeant encourages people to contact their local authority for advice on the appropriate disposal method.