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Promises over the legacy left by London's Olympic Park have been backed by "very few commitments", the Olympic sustainability watchdog has said.
The mechanism to secure the Games legacy must become firmly entrenched, the Commission for a Sustainable London 2012 report said.
However the watchdog's report said it was optimistic about the progress made in some areas.
They praised organisers for "sprinting ahead" on food and waste management.
Commission chair Shaun McCarthy said: "We are very optimistic about the Games' sustainability performance to date."
He said that in terms of progree, the "glass is definitely half full".
"Even before the athletes' arrival we've seen some outstanding performances from the ODA and London 2012 as they sprint ahead on issues such as food and waste management."
He added: "We remain concerned about some of the broader legacy plans, where there have been a lot of promises made about the future of the Olympic Park and knowledge-sharing, but very few commitments made to back up these promises.
"Our priority now is to see that the mechanisms to secure the Games' sustainable legacy are firmly entrenched."