Boat owners and members of the Ipswich Maritime Trust are concerned that proposed changes to the Wet Dock could damage the town's "Crown Jewel".
Following the death of its creator Alan Swann earlier this year, Associated British Ports (ABP) has taken back control of Neptune Marina and plans to integrate it with its own operation.
Ipswich Marina is owned and operated by ABP from the other side of the Wet Dock - from land on the port's "Island Site."
The port owner now plans to extend Ipswich Marina by creating more pontoons for vessels - and to remove Neptune Marina which is accessed from in front of Isaacs on Neptune Quay.
The access to the enlarged marina would be shifted closer to Neptune and Wherry Quays - but the owners of boats berthed in Neptune Marina would no longer have such easy access to pubs and restaurants along the Waterfront.
However in the medium term ABP has ambitions to develop the Island Site - and this move could help to stimulate a new demand there.
Last week boatowners met ABP officials at a meeting in the town, and Ernst Wehden who has a vessel on Neptune Marina said people were very concerned.
He said: "We thought we were going to be presented with a number of options for the future of the marinas. But in the event there was only one plan.
"It was presented as a fait accompli - this is what is going to happen. It's got to go to the borough council by ABP are clearing not expecting not expecting any trouble there."
Mr Wehden felt moving the marina away from its current site would cut off the boat owning community from the town.
He said: "Ipswich is one of the few places in this country where the marina is right by the town centre - that's quite common on the continent but not here. It really is the town's Crown Jewel."
The Ipswich Maritime Trust has not yet had a chance to discuss the proposals, but one of the founders of the Trust, Stuart Grimwade, said there were serious concerns about the impact of chambers on historic vessels.
He said: "The Victor Barge is berthed outside the Old Custom House and is very important to the character of the Wet Dock.
"But there isn't enough space given over to a turning circle for it - there is the bare minimum and the skipper has said it would be impossible to operate it in such a tight area.
"The same would apply for other historic vessels which visit from time to time. There needs to be more discussion about this."
A spokesman for ABP said: "A key focus of our acquisition of Neptune is to improve the experience of berth owners.
"The Neptune team has done a great job of developing their marina over the last 40 years. ABP's ownership provides the opportunity to take marina development in Ipswich to the next level.
"We plan to invest substantially to upgrade marina and waterfront facilities in Ipswich. All berth holders will have options to remain in Ipswich.
"The current configuration is not optimal for either marina or general port operations and single ownership provides a great platform for addressing this. We will engage fully with berth owners on future plans."
A spokesperson for Neptune Marina said “Neptune Marina is immensely proud to have had the foresight some 40 years ago to believe that the redundant Ipswich Wet Dock could be an exciting and attractive place for boat owners and for Ipswich.
"Since launching in 1982 with just one pontoon, so much has been achieved, and the Waterfont has developed beyond recognition. Yet there is still so much potential and now is the time to hand over the ropes to ABP.”
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