Adult supervision is being questioned after a nine-year-old twin drowned in Townsville's Ross River.
The girl's twin sister was saved after they both entered the water and got into trouble late on Monday afternoon, with the dead girl's body being recovered about half an hour after the alarm was raised and onlookers rushed to help.
The inexperienced swimmers were "without adult supervision" and playing "innocently" in a park by the edge of the river when they entered the water, police said.
The girls were in the company of their brother and sister, aged 14 and 13 respectively, and police said the circumstances which led to them getting into the water and the subsequent drowning may have been accidental.
It was "innocent play" turned tragic, Detective Senior Sergeant Dave Miles said.
Police do not suspect negligence, but Det Snr Sgt Miles is concerned about a lack of communication around their supervision.
"Clearly, there were strict instructions they weren't to be near the water," he told reporters on Tuesday.
"What happened appears to be unfortunate circumstances."
The girl's mother was nearby and on the scene inside three minutes of her daughter entering the water, police believe.
They are investigating who was supposed to be supervising the girls and will prepare a report for the coroner.
The girl's death is the third in the river this year after two brothers, aged five and three, drowned in February.
© AAP 2019