A baby has drowned at a popular campsite, prompting police to appeal for information on the "unexplained" death.
Homicide detectives have been called in after the seven-month-old boy was discovered by his mother in the rest area's lake, near Gympie north of Brisbane.
The family were passing through on their way back to far north Queensland, camping overnight at Chatsworth Park about 50m from the water's edge.
The mother called emergency services to the campsite after she found her child unresponsive in the lake on Saturday morning.
Multiple people performed CPR on the baby at the scene before he was rushed to hospital, but the child was declared dead later that night.
Police appeal 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 told reporters on Monday.
"We're actually just investigating further to try and 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."
When asked about claims the child may have been thrown into the water, Det Insp Mansfield said officers could not speculate but hope anyone at the campsite could provide further information.
There was also no indication the incident was mental health-related at this point in time, Det Insp 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.
Det Insp 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 between 9am and 11am on Saturday is urged to contact police.
