Officers were called to Ashby Ville Nature Reserve at around 3pm yesterday following reports for a concern for safety of a boy in the water after he got into difficulty while playing at the reserve.
Specialist officers from the force's underwater search unit conducted a thorough search of the water and found the body of the boy in the water, who had tragically drowned.
Humberside Police are now keen to speak to a man who may have witnessed the event.
Detective Chief Inspector Grant Taylor said: “Our thoughts are with the boy’s family and loved ones at this very sad and difficult time. They are being supported by our specialist trained officers, as they come to terms with the tragic incident.
“The local neighbourhood police team will continue to support and speak to residents in the area and I encourage people to talk to them if they have any concerns.
“As part of our investigation we are now appealing for anyone who may have witnessed the incident to please contact us.
“We’d particularly like to speak with a man who we believe may have seen what happened and hold key information that would help with our enquiries.
He is described as wearing a black polo shirt with grey denim shorts, and is reported to have white hair and a beard.
“If this man was you, or you have any information that would help with our enquiries, no matter how small, please contact us on 101 quoting log 370 of 27 July 2021."