Fairfax County Police say the incident occurred Sunday afternoon at Pirate's Cove Waterpark in the Pohick Bay Regional Park.
Lifeguards cleared the pool around 5 p.m. due to lightning. At that point, the boy was discovered unresponsive at the bottom of the pool.
Police say the boy was taken to Inova Fairfax Hospital and remains there with life-threatening injuries. The incident remains under police investigation.
The waterpark is part of the Northern Virginia Regional Park Authority.
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