The boy was unresponsive when he was discovered by a family member. A neighbour told CBC News the child's grandmother is a former nurse who started performing CPR before emergency crews arrived and rushed him to Lion's Gate Hospital.
He was later transferred to B.C. Children's Hospital.
"These kinds of incidents will often happen very quickly. In fact, they often happen around the dinner hour," said Dale Miller, executive director of the Lifesaving Society in B.C. and the Yukon.
"Mom may be off making dinner. Child is out of sight and out of sound for 10, 15 seconds and they go towards the pool."
Miller said the province needs to implement more consistent bylaws to protect children, like requiring four-sided fencing around pools.
North Vancouver RCMP Cpl. Richard De Jong says parents must take safety around the pool seriously.
"These incidents are very tragic. It doesn't matter what time of year they happen," De Jong said.
"It's an incident where the family is in shock, I'm sure, and we're hoping everything works out for the best."
In April of last year, an 18-month-old toddler drowned in a backyard pool in Deep Cove.