The boy is in the pediatric intensive care unit of the Montreal Children's Hospital.
He was part of a group of children from Sunshine Summer Camp, a day camp that was using the beach.
The camp released a statement Thursday saying its staff is properly trained to react in these situations.
Nevertheless, some parents remain concerned about their children's safety while at camp.
A father told CBC News "you see your child, he goes to the beach and you're worried. Then you get a little phone call – and with the internet, word gets around really fast so it's a bit concerning."
The boy was found in the water at 10:45 a.m. ET by one of the supervisors of the group. He was given CPR by lifeguards before paramedics got to the scene.
Urgences Santé spokesperson Bob Lamle said paramedics managed to resuscitate the boy in the ambulance en route to hospital, where he was met by his family.
Lamle said he has a strong pulse and good blood pressure. He said the next step is to take a brain scan to determine if there is any damage.
Some witnesses at the scene were treated for shock, but were not transported to hospital, police said.
The beach was closed as investigators spoke with witnesses.
Nathalie Lessard, spokeswoman for the park, said the supervision ratios at the time of the incident were respected. There were 64 children in the group and 21 supervisors. That's in addition to the lifeguards stationed at the beach.
She said in the 20 years the beach has been operating, this is the first such incident.
Swimmers were being redirected to the Aquatic Complex in the park.