Goodwin on Sunday afternoon, the Snohomish County Sheriff's Office reported.
The condition of the boy, who is believed to be 15 or 16, was unavailable a couple of hours after the 1:30 p.m. swimming accident, sheriff's Lt. Jeff Brand said.
The teen had been visiting Snohomish County's Wenberg Park southeast of Stanwood with family or friends when he was found submerged in the water, Brand said. Witnesses gave conflicting accounts about how long he had been under. It was unclear why he began having trouble. He was not using a boat or any other watercraft.
After the swimmer was pulled from the water not breathing, a 15-year-old passerby gave him CPR until first aid crews arrived, Brand said. Paramedics rushed the injured swimmer to Providence Regional Medical Center Everett.
The sheriff's office is investigating.
Through last week, Snohomish County had nine drownings this year.
They include an 18-year-old man who drowned July 1 on the Skykomish River near Index and a 10-year-old boy who drowned June 30 on the Stillaguamish River in Arlington.
The Sheriff's Office received a report of a possible drowning near Darrington on Friday, but concluded it was likely a false 911 call after searching the area for hours.
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