Queenstown’s council’s still trying to understand how partially-treated effluent made its way from one of the Shotover wastewater treatment plant’s oxidation ponds into a nearby ‘‘natural swamp’’ on Monday.

Contractors rushed to the site, bordering the Shotover River, to resolve the issue — in a statement to Mountain Scene on Wednesday, acting property and infrastructure GM Simon Mason says they ‘‘remain confident’’ the spill was fully contained within the swamp, and nothing entered the river.

He says the material in the pond that overflowed has ‘‘typically’’ been through 80% of the normal treatment process.

Contractors managed to bring the pump back online, allowing them to pump effluent to the dispersal field in the normal way, while part of the Shotover Delta Rd which was affected, and closed for a time, had since been sanitised and cleaned.

‘‘The swamp has soaked up the spill with no further action required,’’ Mason says.

For now, though, the council’s asking people not to leave the walking track and avoid the swamp area at the delta where signs are in place.

‘‘We’re still working to confirm exactly why and how this situation occurred, but the weekend’s heavy rain and a control system issue are likely to be the key issues.’’

Otago Regional Council’s pollution team’s investigating the incident.

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