LA MESA, Calif. (AP) — A toddler has drowned after falling into a backyard pool in San Diego County while his parents slept.

La Mesa police say parents of the 2½-year-old boy discovered him in the pool Tuesday morning after they woke and found he wasn't in his bed. The boy was declared dead at a hospital.

Police tell KNSD-TV (http://bit.ly/2hmgViq ) that the parents put the boy to bed Monday night but he must have left the bed and made his way to the unfenced pool.

A sliding glass door separates the house from the pool. La Mesa police Lt. Chad Bell says the parents believed they had locked the slider and it's unclear how it was opened.