Green Party co-leader Russel Norman has been keeping a close eye on Rotorua, especially in terms of water quality.
Dr Norman was in Rotorua yesterday attending the International Water Association's 15th International Conference at the Energy Events Centre.
He said Rotorua had a long way to go to get its lakes back to pristine condition.
"The Bay of Plenty Regional Council has been pretty active and the input from Waikato University's David Hamilton has made a significant difference.
"But what we're discussing is that while there is a lot of intensive management you can do, the ability to clean up the lakes without reducing diffuse pollution [from farm run-off, animal faeces, fertiliser] is quite limited.