The boy, part of a group from Winters Flat Primary School, got into trouble when swimming at the pool about 2pm Monday.

He was rescued by a life guard and was later taken to Bendigo Hospital, where he remained in a stable condition Monday night.

The off-duty life guard, who did not want to be named, said the school children were too young to be allowed near the deep end.

"I'm pretty disgusted about what happened," he said.

“The deep end is three metres, they’re too small to swim at the deep end.

“It’s just a big no-no.”

The man, a senior lifeguard and swimming instructor at another pool in central Victoria, said he had dropped off his 13-year-old daughter and her 12-year-old friend at the pool when it opened, and gone to the skate park.

At the skate park he heard children talking about a Facebook post about a drowning at the Castlemaine pool and he rushed back to the pool.

“I was terrified,” he said.

His daughter and her friend were swimming in the deep end of the pool when the incident occurred.

The two girls said they saw the school children swim towards the deep end and it appeared the boy could not swim. The children were not wearing life vests, the daughter said.

Her father said he could not understand how it had happened.

“There were lifeguards and half a dozen teachers as well,” he said. “It should not have happened.

"Someone failed in their duty.”

Bendigo YMCA chief executive Michael Bailey said a formal internal investigation had begun into the major incident.

An external investigation involving Life Saving Victoria and insurers would also be requested.

“It’s in its early stages,” he said.

“At this point our main concern is for the welfare of the boy.”

He confirmed that a Bendigo YMCA lifeguard had pulled the boy out of the water when he got into trouble. Once out of the pool he had spat water out and was able to breathe.

He said the lifeguards had several years’ experience and had done everything they should have done.

Asked about the off-duty lifeguard’s concerns that the children were too young to swim in the deep end, and that the boy could not swim, Mr Bailey said he was not sure yet what had happened but that “life guarding depends on risk, not swimming ability”.

EARLIER: The Bendigo Advertiser believes a boy, who was pulled from the Castlemaine Pool this afternoon, was bobbing up and down in the water when he was rescued. 

An anonymous source has said the school group was in the pool for four minutes when the incident occurred. 

"The lifeguard asked if the boy was alright and pulled him out," they said. 

"He spat the water out."

It is believed the boy was under the water for 30 seconds to two minutes. 

EARLIER: AN eight-year-old boy has survived a near drowning at Castlemaine pool this afternoon. 

Police have confirmed the boy was swimming with a school group at Castlemaine Swimming Pool at about 2pm today when he "got into trouble in the deep end". 

Castlemaine Sergeant Peter Lukaitis said the boy was seen by fellow students lying on his side in the water.

He was immediately pulled from the water by a lifeguard. 

"He was unresponsive so the lifeguard treated him beside the pool," he said. 

"I'm not sure what they did but he was able to walk to the ambulance."

He said an air ambulance responded to the event, but the boy was not transported to the Royal Children's Hospital. 

The boy was taken to Bendigo Hospital in a stable condition.

An Ambulance Victoria spokeswoman said it was hard to tell how much damage had been caused. 

"We believe the boy was under the water for two minutes," she said. 

The Castlemaine Swimming Pool has refused to comment.