Lake Rotorua public health warning remains after wastewater overflow

A sign warning the public of the wastewater leak in Ngongotahā. Photo / Andrew Warner

A public health warning remains in place for Lake Rotorua in Ngongotahā following a wastewater overflow last week.

Rotorua Lakes Council says the warning will remain in place until bacteria contamination levels have reached and stay below the recommended level for safe swimming.

The overflow took place on the evening of Monday, October 18. A public health warning was issued last Tuesday and the council estimated up to 20 cubic metres of wastewater may have reached the lake over three hours.

The council learned of the overflowing maintenance hole, near Arnold St and Waiteti Rd in Ngongotahā, on October 18 about 7pm. It has since admitted there was a delay in reporting the leak to the Bay of Plenty Regional Council and blamed "human error".

Tests over the weekend have confirmed a drop in bacteria contamination levels, however, they have not reduced enough to remove the warning.

Further investigations into contamination levels will need to be carried out before the warning is lifted, Council's three waters services manager Eric Cawte said.

"The lingering levels of bacteria in the water that our tests are picking up are not consistent with what we would typically see following a limited overflow into a large body of water.

"Normally, after a few days, the contaminants linked to an overflow would disperse and diluted into the lake and the bacteria levels to reduce to below the recommended safe swimming levels.

"What we are seeing is slightly elevated levels of bacteria around the Waiteti stream mouth, further upstream and in areas that are quite some way from the overflow site. We are considering whether there are other factors contributing towards the elevated levels."

To help determine the reason for these findings, Council said it was communicating with Toi Te Ora Public Health and the regional council to assess and analyse the current test results.

Last week, Cawte told Local Democracy Reporting once the overflow was stopped the relevant authorities were "notified immediately", with Toi Te Ora Public Health contacted during the response.

"Contact with [the] regional council was delayed until the following day. This was due to human error and is not usual practice."

He said the overflow was stopped by 7.33pm on Monday, the area around the overflow disinfected and signs installed at 7am on Tuesday.

"Once more information was able to be gathered, a public health warning was issued across [the] council's digital channels as soon as possible."