The ArcelorMittal Orbit tower lost more than £500,000 in just a year, as visitor numbers to the attraction dwindled.
Labour London Assembly member Len Duvall said the tower lost £520,000, the equivalent of £10,000 a week, in 2014-15 despite forecasting a profit of almost £1.2million in its business plan.
The London Legacy Development Corporation responded by claiming the Orbit is establishing itself as a top tourist attraction.
The Orbit opened to the public on April 4, 2014. Mr Duvall said its first year financial accounts, published by the London Legacy Development Corporation, showed that despite being expected to generate £1.2million in 2014-15 the Orbit actually lost £520,000, falling short of expectations by £1.7m.
The analysis showed only 124,000 visits were made to the Orbit between April 2014 and March 2015.
The Orbit was commissioned by Mayor Boris Johnson in 2008 and cost £3.1m to build.
Len Duvall said: “With the Mayor’s Olympic Park Orbit tower losing over half a million pounds last year it’s clear that this is yet another Boris Johnson vanity project of towering proportions.
“Instead of paying back some of the £3m of taxpayer investment the Orbit is actually losing £10,000 a week, an awful record even by Boris’ standards. It looks like we can now add the Orbit to the growing list of failed Boris Johnson pet projects alongside the Thames Cable Car, Estuary Airport and fault riddled Boris Bus.
The Mayor’s office has been contacted for a comment.
A London Legacy Development Corporation spokeswoman said: “The ArcelorMittal Orbit was one of the standout successes of the 2012 Games and has seen almost 200,000 visitors since reopening in 2014, which is a tremendous achievement.
“It is establishing itself as a popular visitor destination. As with any attraction, we are constantly looking at ways to enhance the experience to attract more people to this iconic landmark.
“Hundreds of thrill seekers have already abseiled from the top of the sculpture and we’re excited at the prospect of welcoming thousands more to experience the exhilaration of riding the world’s longest and tallest tunnel slide, experiencing a new way to engage with the ArcelorMittal Orbit.
“In the coming years the Stadium and Olympicopolis will be fully open and drive additional visitors to the Park, many of whom will want to visit the ArcelorMittal Orbit.”