A clean-up of Taupō's lakeshore and Waikato River has begun this morning after 80 percent of the town's wastewater spilled into the lake over an hour and a half yesterday.
A water main on Lake Terrace burst, creating a washout which collapsed part of a footpath and took out the sewerage line beneath.
Taupō District Council chief executive Gareth Green told Morning Report today the waste had spread along 200m of the lakefront and down Waikato River.
"We think there's probably 190,000 litres of wastewater went into the lake at that particular point, so yeah, very considerable spill by any stretch of the imagination.
The flow had been shut down early evening yesterday, he said.
"There's no more sewage going into the lake, however the solution that we've got in place is only a temporary fix so we are having to ask residents to conserve water and to reduce their flushing.
"The normal morning peak that comes through the pipes we would struggle to be able to cope with a normal flow.
He said they would be working with Waikato Regional Council and Tūwharetoa Trust Board - which owns the lakebed - on the clean-up.
"In some ways nature will take its course and will be the best thing to be able to solve the problem but there will be some cleanup of things that we can physically do down there as well."
However he said there should not be too much impact on water life because of the size of the lake and the current produced by opening up the control gates yesterday.
"Obviously you've got a whole lot of nutrients which went into the lake that certainly shouldn't have been there - that's not ideal and will create some weed growth and things in that area which is where we'll take some advice from the experts today."
Mr Green said it would only be days - weeks at the most - before people could swim in the lake if they wanted.
"No longer than that would the levels be over the recommended contact levels.
"I guess in some ways we are fortunate ... that it's the middle of winter, so obviously I think the lake temperature's about 10 degrees Celsius so nobody is swimming at the moment which is a small mercy, I guess."
"Most importantly is around the cleanup that is going to be required around the lakeshore and into the Waikato River, where the pumice and now effluent has [flowed].
He said a permanent repair for the sewerage pipe could be weeks or months away.
Taupō Mayor David Trewavas said the spill happened close to the Waikato River mouth and Mr Trewavas said the spillage is flowing down the river now.
Mr Trewavas said water quality testing will occur every hour.
He said the pipe that burst was new and was meant to have a 100-year lifespan.
"You can never know just what's going on down below. We are a geothermal area."
"Lake Taupo is a national treasure and we hold it dearly to our hearts. We're hurt here, in Taupo, that's for sure."