Det Insp Andrew Naismith, from Greater Manchester Police, said: “This is an incredibly tragic incident in which a young girl has lost her life, and my thoughts are with her family at this devastating time.
“We have a team of detectives working on this, but there are not believed to be any suspicious circumstances at this time.
“With the warmer weather, it’s tempting to go into the water to cool off, but I’d like to remind everyone of the dangers of playing near or swimming in rivers, lakes and reservoirs and would strongly urge against this.”
Greater Manchester Fire and Rescue Service watch manager Steve Wilcock said: “When the crews arrived on the scene, there were two other children who had seen their friend disappear in the river.”
Mr Wilcock said the river was more than 20ft deep in parts.
He added: “I would really emphasise to children not to play out in open waterways.
“We would also say to parents, know where your children are, know what they are doing.”
UK weather: 12-year-old girl dies whilst playing in river with friends as heatwave sends temperatures soaring – The Telegraph