Police searching for missing seven-year-old Daniel Entwistle are using sonar equipment to search a river bed.
It will enable police to trace any objects on the bottom of the River Yare in Great Yarmouth, Norfolk.
A bicycle believed to belong to the youngster, who has been missing for four days, was found abandoned by a harbour wall on the river.
The equipment, operated from a boat, is searching from the mouth of the Yare at the North Sea for a two-mile stretch of the water, which
can be up to 20 feet deep.
The search may be continued up to Breydon Water, where the rivers from the Norfolk Broads meet and lead into the Yare.
The search for Daniel
Aerial view of key locations
The equipment will provide a computer image of the riverbed and can search up to 10 miles a day.
Detective Superintendent Julian Gregory, who is leading the hunt said: "We want to make contact with people who use the harbour for recreational fishing, whether or not they were there over the weekend. Please contact us.
"There are people who use the river who may have seen or heard something in
the past or over the weekend that may be of relevance to us.
"One of the options is, he has come to harm because of criminal activity."