A pond at a Bay of Plenty wastewater treatment plant has overflowed into a Rotorua stream.

On its website, Rotorua District Council says there has been a very high inflow into the Wastewater Treatment Plant yesterday and overnight, which again exceeded the rate at which our pumps can pump treated wastewater to the forest.

"That has caused an overflow of the pond which stores treated wastewater and from where it is pumped to the forest. The treated wastewater – which has been further diluted by rainwater – has flowed to the Puarenga Stream."

The pond started overflowing at about 4am today and the pumps are working at full capacity in an effort to stem the overflow. All systems at the plant are operating at capacity.

"According to MetService, we are expecting continuing rain today. Any easing up of rainfall will assist in helping to control the situation at the treatment plant, however, more heavy rain is expected over the next 12 hours," says the council.

The situation is the same as that which occurred last month following two weather events within one week.

Excess amounts of rainwater have flowed into the sewer network and gone through the treatment plant, along with wastewater, which has exceeded capacity and caused the overflow.

"Council will over the next few months review its programme to identify where stormwater is entering the wastewater system. However, this will not be a quick process and there is no temporary fix.

"The proposed upgrade of the wastewater treatment plant will increase the plant's capacity and treat wastewater to even higher levels, reducing the potential for such incidents to occur in future."