Charlie Dunn, from Tamworth, Staffordshire, was pulled from the Blue Lagoon at Bosworth Water Park in Leicestershire on Saturday afternoon.
He died later in hospital and a man and woman were arrested.
Police declined to give any further details about the pair.
The man and woman, who are believed to be Charlie's mother and stepfather, have been released on bail pending further inquiries.
In a statement, Leicestershire Police said: "Our investigations in to the circumstances surrounding the death are ongoing.
"We would continue to ask people not to speculate about the incident and the circumstances around the death and leave the authorities to carry out their investigations."
Officers are urging witnesses and anyone with video footage taken at the park to come forward.
Witness Olivia Quinn said the scene at the water park was "horrific".
"It hasn't left my mind seeing the boy's body on the ground and seeing people try to save him by giving him CPR," she said.
"Everyone was in shock, crying and praying for the little boy. The ambulance took a while to come as it was so busy with people everywhere and cars all around the park."
She said people got towels to "cover him and give him privacy" and "were trying to get their children not to look".
The park reopened on Sunday, with owner Nigel Riley describing the incident as "dreadful".
A statement on its Facebook page said: "From all of the staff at Bosworth Water Park we would like to pass on our deepest sympathies to everyone affected by this tragic loss of life."
Source: Bosworth Water Trust website
Two people arrested over the death of a five-year-old boy in a suspected drowning at a water park were held on suspicion of manslaughter by gross negligence, police have said.