Squatters stole up to £2,000 worth of equipment from a boat moored in Wisbech yacht harbour – and other craft have been broken into.
Trevor Bunn said: "Boat owners have been emailed by the harbour office to inform them there are homeless people squatting on boats moored in the marina.
"I was alerted last Thursday to find my boat broken into and around £1,500 to £2,000 worth of effects stolen."
Fenland District Council, that runs the yacht harbour, is meeting police to discuss "preventative action".
Mr Bunn said: "I spent several days repairing the damage to my boat and was witness to others who have suffered similar losses.
"There is little sympathy from the management of the marina who simply point out it is my problem for having inadequate insurance to cover losses resulting from a break in.
"The thieves went through every locker removing gear and even opened a container in one which contained my late brother's ashes."
He said he was "deeply upset and angry with the lack of professionalism shown by the marina's management who are employed by the council. Their performance needs investigating."
A council spokesman said: "There had been some anti-social behaviour from an individual rough sleeping on a boat; he has since left the premises and the police are aware.
"There have been a number of boats broken into recently but we don't know if they are connected."
The spokesman said the council is increasing the number of walk through inspections "and our CCTV service has increased the number of times they pan the yacht harbour.
"Last week security fencing had anti-climb paint reapplied and we are in the process of making amendments to some of the lower level fencing around the yacht harbour."
The spokesman said council officials are meeting with local police to discuss some preventative action where police increase foot patrols to include the yacht harbour.
"We have recently advised boat owners to be extra vigilant when keeping personal possessions on board their vessels and to ask that anyone affected to please let us know and contact the police for a crime reference number," said the spokesman.
Wisbech yacht harbour advertises "safe, secure moorings within the River Nene."
It has 128 marina berths.
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