Fifty-one young people died when the pleasure boat Marchioness collided with a dredger and sank in central London in the early hours of August 20 1989.
Survivors and families of the victims joined a procession from Southwark Cathedral to Bankside, next to the site of the accident, where a short service was held by the Bishop of Southwark.
The names of those who died were read out and petals were thrown into the water.
Boats from the Royal National Lifeboat Institute, the fire and rescue service and Port of London Authority gathered on the river for the crews to pay their respects.
Most of those on board the Marchioness were high flyers from the finance and fashion worlds.
Odette Penwarden, 72, of east London, spoke about how she survived the sinking.
"The dancing was in full swing when all of a sudden the boat lurched," she recalled.
"The boat started to tip over. Water came rushing in and knocked me off my feet. It was like going inside a washing machine.
"I could feel myself losing consciousness, but I had an image of my mother and I decided I needed to get myself out."
Ms Penwarden managed to escape through a broken window and was rescued by a police boat.
She added: "It took a couple of days for me to realise how many people had died, and that I had been so lucky to have survived."
Andrew Dennis, 54, of north London, attended the service to remember his brother Howard and four friends who died in the tragedy.
He expressed his "disbelief" that the boats and bridges on the Thames do not have more safety lights.
"It's so simple," he told the PA news agency. "It's not even 9 o'clock and already you can barely see.
Following the death of his brother, Mr Dennis said he spent the following weeks in Paris.
"Whilst I was up in the Eiffel Tower on New Year's Eve it saddened me to the core, you could literally see all the way down the River Seine because everything had luminous tubing on it.
"You think 'why can't they put that on every bridge?'.
"Thirty years ago, 51 people have died and it's still dark. You should be able to see all the arches of the bridges, all the outlines of the boats."
"That still riles me all these years later."
Mr Dennis said there is a "lovely companionship" among the relatives of the victims and the people who survived.
He added: "There's nothing to explain because everyone is suffering the same."
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