A baby has drowned at a popular Queensland campsite, prompting police to appeal for information on the “unexplained” death.

Homicide detectives have been called in after the seven-month-old boy’s mother found him in the lake at a rest area near Gympie, north of Brisbane, on Saturday morning.

The family were returning to far north Queensland and had camped overnight at Chatsworth Park, about 50 metres from the water’s edge.

The mother called emergency services after she found her child unresponsive in the lake.

Multiple people performed CPR on the baby at the scene before he was rushed to hospital. He was declared dead later that night.

Police have appealed for anyone who stayed at the park and left on Saturday morning to come forward.

“We’re treating this as an unexplained death,” Detective Inspector Craig Mansfield said on Monday.

“We’re actually just investigating further to try to establish why and how this incident occurred. So we’re hoping that those people who have left the scene or were in the vicinity might be able to assist us with that.”

Asked about claims the child may have been thrown into the water, Mansfield said officers could not speculate but hoped anyone who was also at the campsite could provide further information.

There was no indication the incident was mental health-related, Mansfield said.

“We just want to complete that full picture before we decide on where the investigation leads us,” he said.

The child’s parents are assisting police with inquiries.

Mansfield said the mother had not been able to tell police how the child ended up in the water.

“The mother of the child did retrieve this child from the water. It’s been a very traumatic experience for her clearly,” he said.

“There’s missing parts leading into [the child’s death] that we need to try to establish and square away. This is the part where we need public assistance to ascertain exactly how that occurred.”

Anyone at the rest area off Gympie Curra Road between 9am and 11am on Saturday is urged to contact police.

-AAP