Campaigners say vital safety measures, including life-saving equipment and tighter regulations on who can sail boats, which were supposed to have been introduced after the Marchioness river boat disaster 10 years ago, have not been implemented.
The Thames will be a focus for the new year festivities with two million people expected to attend bankside celebrations on New Year's Eve. And a million visitors are expected to use river boats to visit the Millennium Dome throughout 2000, according to its organisers.
Despite this, most bridges over the river have no safety equipment. Life buoys, which should be installed at regular intervals along the riverside, are dotted along the bank intermittently.
Southwark Council, which administers a large stretch of the south bank, claims it is not responsible for such matters - but it said that it had installed some life buoys and safety chains "following recent incidents and in particular in the anticipated huge attendance at the millennium celebration".
Another authority, Hammersmith and Fulham Council, says it has no plans to install life buoys or other safety equipment on the riverside or Hammersmith bridge.
"We do not have much use of the river here," said a council spokesman. Emphasis instead is put on prevention, with fences and warning notices. Campaigners have asked for loop chains to be installed along riverside walls and around bridge supports, allowing anyone who falls into the water to hold on until help arrives. There are chains alongside Battersea Park where the walls are particularly sheer. But few other locations have them.
Margaret Lockwood Croft, of the Marchioness Action Group, who lost her son Shaun in the 1989 disaster, said: "I think it is inexcusable that many of these problems were known, even before 51 people died on the Marchioness, yet even now nothing has been done."
Gareth Pierce, a solicitor who represents survivors and families of the victims, yesterday condemned the decision to hold the millennium night celebrations on the Thames.
She said: "The most foolhardy gesture that could have made to celebrate millennium night was to deliberately congregate as many people as possible on a dangerous waterway at night, where there has been a catastrophic disaster which remains still unresolved in terms of safety, rescue or who was in charge."
In September, the Secretary of State for Transport, John Prescott, appointed Lord Justice Clarke to head an inquiry into Thames river safety. Many groups and individuals have already raised major concerns over safety in their submissions to the inquiry.
Mr Prescott requested that the inquiry's interim recommendations be delivered in time for the millennium. But even if recommendations are made it is unlikely that any could be implemented in time.
And there are other worries about the celebrations: currently there are no proper drink-drive laws applicable to river users; inexperienced sailors are allowed to navigate the tidal Thames unsupervised; and no organisation has overall responsibility for search and rescue on the river.
Superintendent Rob Glen, a former head of the river police, said yesterday: "When I was at the Thames police I suggested the same laws should be implemented as on the road. This was strongly resisted by river users."
The former Newham South MP Nigel Spearing, who has been navigating on the Thames since 1943, told Lord Justice Clarke's inquiry: "Many of us have been asking for chains for the last 10 years, but nothing has been done."
But the biggest unresolved safety issue is that no organisation has overall responsibility for search and rescue on the Thames. Although various organisations including the Port of London Authority, the Metropolitan Police and the fire brigade all have boats which undertake rescues, all make clear that search and rescue is not their responsibility.
Chris Pond, MP for Gravesham, said commercial pressures appeared to have compromised safety in recent rail and other major accidents, adding: "It would be a travesty if this this were to happen on the river Thames too. The stakes are far too high as the families of the 51 victims of the Marchioness disaster will testify."