Scientists warned government officials decades ago that trouble was brewing in Rotorua's lakes - but they were ignored.
Rotorua and the country's taxpayers are now paying the price, they say.
If action had been taken then to keep Rotorua lakes in good health, problems now costing millions to fix may havebeen prevented, or at least lessened, says Freshwater Sciences Society president Neil Deans.
He told the Daily Post a Government scientist warned central Government in 1972 that Rotorua's lake water quality would degrade if pastoral development didn't slow down, but nothing was done.
"Researchers predicted some of the current issues decades ago, but their message was not addressed by most authorities at that time. Now the costs of clean up are in the tens of millions of dollars," Mr Deans said.
He wasn't sure why no action was taken but said if something had been done it would not now be costing $190 million to fix up the lakes.
"I presume it wasn't regarded as an important issue. It may not have got in front of a politician who could've made a difference," he said.
Mr Deans said research into what could be done to help the lakes and then doing something about it was the key and scientists had a responsibility to make sure their concerns were listened to. "It's very well doing research but they need to make sure the right people know and understand."
Mr Deans said it wasn't until the summer of 2002/2003, when the whole of Lake Rotoiti was closed for swimming, that people took notice of the deteriorating water quality.
"That's serious stuff. That also made the politicians realise that this was a really serious [problem]."
The state of the region's lakes is being discussed at a national Freshwater Sciences conference in Rotorua this week.
