Otago Regional Council (ORC) is investigating a wastewater overflow near the Lake Dunstan Cycle Trail, as Central Otago District Council (CODC) admits some public warning signs erected at the site last week were put up "overenthusiastically".

ORC compliance manager Simon Wilson confirmed CODC reported the incident to the regional council’s pollution hotline on Monday (December 8) morning.

“As the matter is subject to a current investigation, we are not able to provide further comment at this time,” he told The Central App.

A spokesperson for CODC’s water services team said a split in the wastewater main between Lowburn and Cromwell that resulted in “wastewater liquids” breaching the line.

The leak is believed to have started on the evening of Sunday (December 7), and was reported by a member of the public to a council contractor, who attended the site shortly afterwards.

“It is currently undetermined how the pipe failed, however, the pipe will be sent away for testing to assist in determining condition and the potential cause of the pipe failure,” the spokesperson said.

The total volume of wastewater released is not yet known. CODC said its contractor is preparing a report, which will include an estimated volume and be shared with ORC before being made public.

CODC also addressed confusion around warning signage erected last week near the cycle trail and lake, a few hundred metres from the Kiwi Water Park, which temporarily prohibited swimming and contact with the land.

The spokesperson said some signs were unnecessary as there was “not believed to be a risk to public health”.

"Unrequired precautionary measures were taken by erecting both 'No swimming' and 'Do not enter' signage in the vicinity of the area. This was admittedly done overenthusiastically, but with good intent," they said.

Because the signage was already being discussed on social media, the council chose to retain a small number of 'Do not enter' signs, relocating them to a contained area measuring 15 metres by 15 metres. 

The spokesperson said this approach was taken for "transparency", as removing all signs quickly may have raised further community concerns.

The affected site is well away from the track and there is no cause for concern for people using the track, they said.

“There is potential residual contamination on the land, however the discharge was liquid only and the area has had a thorough cleanup from our contractors,” the spokesperson said.

“Bunding was formed and a ditch was dug in the discharge flow stream to prevent the liquid from getting to the lake. Hydro excavation trucks were used to remove the liquid and spoil from the site.

“Contractors confirmed that the discharge did not reach the lake. Precautionary sampling was undertaken, including samples near the water park to ensure public safety. All results confirmed no contamination.”