A toddler is in critical condition in hospital after he was found unresponsive in a lake in Hampshire.
Firefighters pulled the two-year-old boy from Swanwick Lake, a nature reserve near Fareham, on Sunday night.
Hampshire Constabulary said its officers, the fire service and paramedics were called to the lake at 8.21pm.
The boy was taken to Southampton General Hospital, where he is now in a critical but stable condition, the force said.
Detectives have appealed for anyone who was nearby between 7.45pm and 8.30pm to contact them.
Detective Inspector Toby Elcock said: “We know this incident will come as a shock to the local community, but we ask people to please not speculate as we follow up all lines of inquiry to establish how the boy came to be in the water.
“We are keeping an open mind as to what has happened, and we are keen to speak to anyone in the area to help us build up a picture of the circumstances.
“If you were in the area at this time, please call us. Any information, no matter how small, could prove significant, so please do get in touch.”
An 18-year-old man from Southampton, who officers said was known to the boy, has been arrested.
Anyone with information should call police on 101 quoting the reference 44210210811, or Crimestoppers anonymously on 0800 555 111.
Additional reporting by PA
