Police are today trying to identify the bodies of two people found on board a boat on the River Bure by Wroxham Broad.
They were discovered shortly after 4pm on Thursday by emergency services after concerns were raised about the length of time the boat had been moored in one spot next to Wroxham Island.
When police stepped aboard the boat, they found the two bodies as well as a dead dog.
Detectives, including officers from Great Yarmouth CID, are investigating the deaths.
They are currently being treated as unexplained.
The boat was a small, white motor cruiser and is believed to be privately owned.
Police asked that the boat's name and registration number were not revealed to avoid identifying the victims before their next-of-kin had been informed.
The coastguard sent four boats to the scene to help other emergency services.
A spokesman said: 'About 4.15pm today, East of England Ambulance Service asked the UK Coastguard for assistance at an incident outside Norfolk Broads Yacht Club at Wroxham.
'The ambulance service reported that two persons on board a white sports boat appeared unresponsive and they required support to secure the vessel so that they could provide medical assistance.'
Coastguard rescue teams from Happisburgh, Mundesley and Winterton were called in, as well as the Hemsby Broads rescue independent lifeboat.
The Hemsby boat was launched from a public car park next to the yacht club, from where investigators clad in orange suits could be seen aboard the vessel where the bodies were found.
Police cordoned off a stretch of river around Wroxham Island while the investigators were at work.
Holidaymakers in their own pleasure boats were forced to divert around the area and take another route around Wroxham Broad.
Seven fire engines were called to the scene, as well as a fire service surface rescue boat and its environmental health unit.
Roy Harold, Norfolk chief fire officer, said they had a 'range of crews attending to help police and ambulance'.
A fire service spokesman said it was originally thought to have been a 'hazardous materials incident'.
The East of England Ambulance Service attended with two crews and one officer.
Tom Garrod, a Norfolk county councillor for Wroxham, said that while the investigations into what happened were at an early stage, he would be looking to what the police found out to see if there were any 'lessons to be learned' from the tragedy.
Mr Garrod said he wanted to pass on his condolences to the family of those involved.
Anyone with information about the deaths should contact the police on 101 or, anonymously, Crimestoppers on 0800 555 111.
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