The mother of two young boys who drowned in Townsville in February has been arrested on two counts of manslaughter.
The bodies of five-year-old Barak Austral and his three-year-old brother, Jhulio Sariago, were found in the Ross River in the wake of the Townsville floods after a frantic search.
Their 47-year-old mother was taken into police custody on Friday and is expected to be formally charged over the deaths, along with unrelated drug trafficking offences.
Townsville police said the deaths could have been avoided.
"This is a catastrophic result for this family and it is a preventable tragedy," Detective Senior Sergeant Miles told media on Friday.
"These boys were aged three and five - they should’ve been adequately supervised, they should not have been allowed to roam anywhere near any large body of water let alone the Ross River, given what the circumstances were."
Police said they had chosen to arrest the mother on the more severe charge of manslaughter after their investigation revealed "gross negligence" over a prolonged period.
Gracelyn Smallwood, an Aboriginal activist based in Townsville, told NITV News the community was "in shock".
Ms Smallwood said she didn't want to lay blame for the tragic deaths, but claimed the Queensland Department of Child Safety (DOCS) had questions to answer.
"This doesn’t happen overnight, and DOCS need to be investigated on what role they played for the safety of the children," she said.
The Biri woman reiterated her thanks to the Townsville community for helping to raise funds to transport the boys' bodies home to Darwin for their funeral.