The geologist who blew the whistle on Rotorua's declining geysers in the 1970s has warned against plans to relax restrictions imposed on private geothermal bores in 1986.

Former district geologist Ted Lloyd, 73, says the famous Whakarewarewa geysers are still far from their former glory.

"Apart from Pohutu, which never stopped, no geyser that stopped before the bore closures has recovered, and several have stopped since the bore closures," he said.

Environment Bay of Plenty principal environmental consents officer Brett O'Shaughnessy painted a much rosier picture at a conference in Taupo, noting that the total geothermal heat flow in the Whakarewarewa field dropped from 20 megawatts in the 1960s to 14MW in the mid-1980s but was now back up to 19MW.

The agency is due to receive a report this week from consultants at Industrial Research on scenarios for relaxing some of the restrictions imposed 18 years ago.

But Mr Lloyd and a retired Auckland University physicist, Associate Professor Ron Keam, said most of the geysers that earned Rotorua its reputation were still dead.

"Papakura geyser, which used to be going all the time, has not gone for decades now," Professor Keam said.

"Waikite geyser, which you see going along Fenton St, has just got steam coming out of it. It hasn't had water for close to 30 years.

"Wairoa geyser was the biggest one in Whakarewarewa. If it has any water, it's acid water. It needs alkaline water for that geyser to be going."

Mr Lloyd said the Kereru geyser, on a low terrace near the Puarenga Stream, had stopped since 1986, and the Roto-A-Tamaheke thermal area east of the main tourist tracks had failed to recover.

One possible cause of the continued weakness of the geysers was that much of the water in the Puarenga Stream was escaping underground between the main bridge at Whakarewarewa and a bridge downstream near Forest Research.

"In my opinion, what has happened here is that the underground pressures have decreased to the point where [cold] stream water can get down into the hot springs," he said.

"It took 40 to 50 years to run the system down. It's not going to recover overnight.

"I certainly think they shouldn't be contemplating increasing the exploitation again until one is absolutely sure what's happening."

Mr Lloyd was district geologist in Rotorua for the former New Zealand Geological Survey at the time when restrictions were imposed in 1986.

"It all started off with me but there were lots of people involved," he said.

"It would be 10 years from the time we advised the Rotorua District Council that there was a problem before anything was done, and in the end the Government had to step in because the local council decided they couldn't handle it."

The Geological Survey was absorbed into a new Institute of Geological and Nuclear Sciences soon after Mr Lloyd retired in 1990. Its Rotorua office was closed.

Environment Bay of Plenty scientist Dougall Gordon said thermal activity had always moved around the Rotorua field, so some specific geysers that were active in the past might not come back even though the overall field had recovered.

"We may never get those ones back. That's just the nature of the beast."

He confirmed that some water was escaping underground from the Puarenga Stream and said the agency was unlikely to recommend any relaxation of the present restrictions after receiving the consultant's analysis of a computer model of the field.

"At this stage we'll probably stick with the status quo unless the model can tell us otherwise," he said.

The ban on private bores within 1.5km of Pohutu geyser is expected to remain.