A floating river park championed by Boris Johnson will not be completed in time for the Olympics and will have to be redesigned if it is to go ahead, its developer admitted today.

The Thames river park project, which has attracted hundreds of complaints from residents, would have been a public walkway on a linked series of pontoons running from the Millennium Bridge to the Tower of London.

It would have included a lido and a jetty for ferry services. The Mayor last year gave his backing to the £60 million project and called it "design brilliance".

The park's developers had insisted that it would be completed before the Olympics and the Queen's Diamond Jubilee celebrations, but after a series of delays they have admitted there is no chance of this.

They also conceded that the design would have to be changed to have a chance of securing approval from the City of London Corporation's planning committee. The developers said they would return with new plans in the coming months.

Local groups had voiced concerns about the park and the Port of London Authority said it could impact on the "navigational safety" of the Thames.

The organisers of the 3,000-boat river pageant to celebrate the Queen's Diamond Jubilee also said the river park would force them to reduce the size of the display by one third.

A series of claims was also made about Venus Group, the mysterious foreign backers of the project.

In a letter to residents and businesses, John Naylor, the director of the London River Park, admitted that the scheme was being reviewed. He wrote: "Whilst Londoners as a whole are supportive of the scheme, it is clear that local residents and river users in particular would like us to look again at certain elements of the scheme and consider whether changes can be made.

"We can confirm we are now reviewing the scheme taking into account what we have been told… I can confirm that we are no longer proposing to take the scheme into the construction phase in advance of the Olympic Games."

Leader of the London Assembly Labour group Len Duvall said: "It was obvious when the Mayor rushed in that this was going to be much more complex and difficult to deliver on time than he realised. There are still unanswered questions about this project and the lack of financial due diligence that should be investigated."

Green Party Assembly member Darren Johnson said: "It's no surprise that Boris Johnson's promise of a Thames walkway in time for the Olympics is rapidly fading after fears that it poses a navigational hazard."

A spokesman for the Mayor said: "Protecting and enhancing our cherished waterfront has always been at the heart of delivering this exciting project. It is only right that people's views are being taken into account so the river park has their complete blessing."