Plans for a cycle and pedestrian bridge across the River Thames in east London have been dropped due to rising costs.
The crossing had been intended to run between Rotherhithe and Canary Wharf.
City Hall said final costs may be above £600m meaning the bridge was "currently unaffordable", so alternatives such as a ferry service would be "reassessed".
The London Cycling Campaign charity said it was "most concerned" by the decision, particularly as a road tunnel is due to be built nearby.
Walking charity Living Streets also called the plan "disappointing" as "healthier and cleaner ways to travel should be prioritised".
The crossing was one of 13 announced in 2015 and a public consultation saw 93% of respondents strongly supporting the idea for the cycle bridge.
The decision to drop the plan was revealed in a letter from Heidi Alexander, the deputy mayor for transport, to the London Assembly transport committee.
In it she said explained that "considerable effort" had been made to minimise costs but the "location, the sheer scale and the complexity of the engineering" meant it was not feasible.
The position of the crossing meant it potentially would need to be the world's largest vertical-opening bridge so ships could get pass.
Ms Alexander added that the decision had been made "in the context of Transport for London's (TfL's) wider financial challenges".
Responding to the letter, transport committee Chair Florence Eshalomi said dropping the bridge was "hugely disappointing" as it was "vital to boosting the local economy".
Caroline Russell, Green party member of the London Assembly, called the cancellation "shocking" but said there could be a silver lining if "TfL move fast on alternative schemes" like a free shuttle service.
A spokesperson for London's mayor said ending the plan was the "sensible and responsible thing to do to protect the London taxpayer" and TfL was "exploring options for a new fast ferry".