The leader of an iwi trust is "absolutely concerned" about a wastewater spill into Lake Rotorua.
A public health warning was issued Tuesday and further testing is set to take place after the spill near Arnold St and Waiteti Rd in Ngongotahā.
Rotorua Lakes Council estimated up to 20 cubic metres of wastewater may have reached the lake over three hours.
It said the affected land was cleaned and disinfected, and signs were in place along the beach to warn against recreational activity and swimming.
Te Arawa Lakes Trust chief executive Karen Vercoe said while the trust understood the council was doing all it could to rectify it, the issue should not be minimised.
She was also concerned about when the trust was notified of the spill, saying it would expect "more timely reporting especially to us as the Te Tiriti partner, because these are our lakes."
Jack and Di's Lakefront Motel and Lodge owner Ken Liao was also concerned about the overflow, which occurred opposite his motel.
"Luckily we don't have many guests around our property, only a few people.
"Kids cannot play in the water."
Progress Ngongotahā chairman and ex-councillor Bob Martin said he was not concerned about the spill provided the council were "on to it" and doing its best to fix the problem.
On its Facebook yesterday, Rotorua Lakes Council said a member of the public alerted it to an overflow from a manhole on their property on Monday evening.
Wastewater flowed from the manhole across the ground and made its way into the lake.
"It is estimated that the overflow was happening for approximately three hours before council was alerted to the issue. Trility staff attended immediately and restarted the nearby pump station to manually stop the overflow.
"The cause of the overflow was under investigation. However, initial inspections have found a major fault in the on-site computer that controls the pump station. It is unclear at this stage what caused the fault," the statement said.
Rotorua Lakes Council's three waters services manager Eric Cawte told the Rotorua Daily Post the fault had been identified as a "loss of programming code from the memory of the programmed logic controller".
The council was checking if the issue was related to a power cut in the area.
The pump station was manually restarted and had been operating as normal since 7.30pm on Monday night, he said.
The controller at the station had been re-programmed and had been "operating satisfactorily".
A level sensor for the back-up alarm system had been replaced with a new one as a precaution.
"Where possible the network has backup systems, including monitoring alarms and secondary pumps, and the system continues to be improved as technology and engineering practices evolve," Cawte said.
"However, there are more than 80 wastewater pump stations across the district and there is always a risk that there could be a fault or damage that causes issues with the network.
Investigations and further testing of lake water would continue over the next few days.
The council said relevant authorities including, Te Arawa Lakes Trust, Bay of Plenty Regional Council and Toi Te Ora Public Health have been notified.
Regional Council compliance manager Stephen Mellor said the council was not made aware of the discharge until early afternoon on Tuesday and was therefore unable to attend when the incident occurred.
Rotorua Lakes Council would be providing the regional council with a full report in relation to the incident which would inform any decisions about the discharge, he said.
Mellor said the council had not received any complaints from the public on the matter.
Toi Te Ora Public Health was contacted for comment.
In March this year, there was a wastewater leak around the Parawai Rd pump station nearby.
It was thought about 80 cubic metres of wastewater may have entered Lake Rotorua.