A holding pond that discharged a brown substance in the Waikato River is unlikely to present any ongoing risk to water users, including swimmers after a possible contamination earlier this week.

Landowners and businesses operating downstream of Huka Falls were advised earlier this week to be cautious of the river water after it was polluted by a brown substance.

Reports on Wednesday suggested a wall of a holding pond failed and its contents entered a tributary which leads into the Waikato River upstream from the falls.

Information provided to Waikato Regional Council by Contact Energy indicated the discharge was unlikely to affect the river's users.


A statement from the council said while it was still awaiting the analysis results of samples collected earlier this week by its staff, initial results from GNS provide confidence there would be sufficient dilution in the Waikato River.

The statement said this would have brought contaminant concentrations to well within those typically expected in the river, council scientists have concluded.

Based on this information, council scientists said concentrations of contaminants would be well below levels of concern for both ecological and human health.

While it was likely total suspended solids and turbidity will take longer to return to typical levels, members of the public were unlikely to see any further discolouration of the water as a result of this particular incident, the statement said.

However, discolouration could occur if there was high rainfall over the coming days, as a result of the stream bank erosion caused by the initial incident. The council would continue to monitor this.

Meanwhile, the council was continuing to work with Contact Energy to investigate the incident and establish what caused it.

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