The future of a distinctive houseboat moored on the River Ouse at Lewes is in doubt after its sinking.
The unoccupied, hand-built vessel had been broken into, said Sussex Police.
Various property was stolen before the vessel was apparently cast adrift from the mooring at Southerham Lane, they said.
The incident was reported to police on Monday (February 19) but it is not yet known when it occured.
The 36ft houseboat, The Grey Lady, was built entirely from recycled materials by Jason Pedesto and modelled on a Mississippi paddle steamer.
It was the subject of a dramatic night-long rescue in October 2015 when the craft was in danger of being dashed against rocks during a storm at Southease Bridge.
The RNLI and coastguards arrived in the early hours and managed to get a line on the three-storey boat before spending the rest of the night towing it upriver.
The Grey Lady, stricken at the edge of the Ouse, has been the subject of emergency work this week.
A spokesman for Lewes District Council said: “Working with the Maritime and Coastguard Agency and a local marine engineering company, the boat has been secured to the riverbank.
“The boat is listing and should not be boarded.
“Temporary fencing is being erected until a permanent solution is found.”
A spokesman for the Environment Agency said it was aware of the semi-submerged houseboat on the river.
He said: “The Environment Agency is not responsible for the removal of vessels which come adrift or sink.
“However, we do have ‘permissive’ powers, to intervene if there is a wider public flood risk.
“Currently, the vessel poses a low environmental risk in terms of pollution.
“Also, we do not believe there will be a risk of flooding or damage to river defences, if the houseboat breaks away from its moorings and moves away from the site.
“Nevertheless, we will continue to support Lewes District Council to reduce and address any pollution from fuel leakage and we continue to monitor our flood defences in the area,” he added.