A "really deep" geothermal pool has been discovered on the Rotorua lakefront only two metres away from one resident's home.
But a GNS scientist says the activity is expected and nothing to be concerned about.
Ōhinemutu resident Lani Kereopa, who lives on the lakefront, said she has alerted the Rotorua Lakes Council to the new pool at Te Ruapeka Bay after she watched it develop in recent weeks.
She said the hot pool was only two metres from one of the dwellings on her property and looked like "it is going to get a lot bigger".
Kereopa said the lakefront ground had always been hot and with steam consistently coming from sections of the beach.
But months ago, mud started to appear in some areas and two weeks ago, Kereopa noticed in one area the ground had started to sink.
"Over the past week, it has just gotten deeper. And it seems to have all of a sudden turned into a blue, really deep-looking pool," she said.
"That is when I started to worry because pools, when they are that colour, are pretty deep."
She had contacted the council today , saying she was concerned about foot traffic increasing as the weather improved and fencing needed to be put around the pool.
The geothermal pool was on the beach and fully accessible by the public, she said.
Kereopa said she initially put cones around the muddy area to prevent access, but eventually, they sunk in the pool and had to be removed.
And now there were other sections along the lakefront where the mud was starting to sink into the ground, which was also of concern, she said.
"I am a little bit worried a whole lot of that beachfront is going to become hot pools. But there isn't much we can do - we just have to watch it."
Kereopa said accidents involving geothermal pools were not a common occurrence.
"Because we live amongst it, and we see the changes occurring every day - you kind of know when something is happening.
"I wish it wasn't there - but what can you do? We live in this environment - so we just have to watch it and hope it doesn't get too big."
GNS volcano information specialist Brad Scott described Te Ruapeka Bay as a "traditional site of geothermal activity" at Ōhinemutu.
The heat flow was very high, which meant hot temperatures at very shallow depths, he said.
Many of the springs were boiling - between 97 and 100C - so the temperature at a shallow depth was the same, he said.
The geothermal process would be ongoing and further geothermal features may appear, he said.
But Scott reiterated there was no increase in the level of activity, rather activity had been re-established through reclamations.
He said the area had been infilled/reclaimed over the past decades, with areas of geothermal activity buried during this process.
"With time the geothermal activity will re-establish itself through the reclamations. That appears to be the process happening here," Scott said.
The recent high lake levels were also raising the water level in the area and the geothermal system.
He said generally geothermal features were fenced to stop people from getting too close and he encouraged concerned residents to contact the council.
Rotorua Lakes Council geothermal inspector Peter Brownbridge said it appeared a pool had emerged in an area of reclaimed land at Te Ruapeka Bay.
Brownbridge said the pool may require fencing and people should be cautious when in the area.
He also said it was not an uncommon occurrence as the area was well-known for geothermal activity and features.
Earlier this month, Whakarewarewa Māori Village closed to visitors after a tourist fell into a sinkhole and was seriously injured.
Emergency services were called to the living thermal village after an elderly Australian woman fell into a fumarole (sinkhole) on a footpath. The hole was estimated to be about 2m by 1m wide and 1.5m deep.
Her husband received moderate injuries trying to pull his wife from the hole.
The sinkhole at the village had since been filled in with steam vents installed.