The seriously injured boy was found by a passer-by around noon on Sunday on a lawn between Meanderlaan and De Overloper. He called the emergency services.
Police have launched an investigation at the crime scene. Investigations were also done with a sniffer dog, a helicopter and divers looked for in the water. The police also interviewed several witnesses.
On the day of the stabbing, the police identified two suspects. It concerns two boys who do not live in Middelburg. They are on the run.
The police are calling on young people in Middelburg to stop distributing photos of possible people involved in the stabbing. They are inflammatory and harm the person involved, according to the police.