Firefighters rescued an injured cygnet which had got trapped behind a fence along a bridge off Silvocea Way in Poplar.
The swan had got caught in an inaccessible area alongside the bridge walkway.
Site staff were on the phone to the RSPCA when crews were alerted to his plight by volunteers from The Swan Sanctuary, who realised they wouldn't be able to gain access to free the bird.
Swan Sanctuary volunteer rescuer Helen Stoddard said: "We're not sure how he got in - he may have hit overhead lines or perhaps got blown off course and crashed in.
"The firefighters arrived very quickly and set about finding the best way to gain access. In the end they removed some bolts and managed to pull the grille out enough to squeeze through.
"We gave them a briefing on how to catch him so as not to injure him and control his powerful wings.
"Once they released him we took him to the sanctuary where he is doing well. He had some cuts on his feet but they will heal and he can then be released into an appropriate flock.
"The crew really were wonderful and we're so very grateful they got the poor cygnet freed so efficiently."
A London Fire Brigade spokesperson said: “We would always encourage people to call the RSPCA in the first instance if they see an animal stuck or in distress.
“Firefighters love animals too and we are always happy to assist if our specialist equipment is required, as it was in this case.”
The Brigade was called at 1800 and the incident was over for firefighters by 1858. One fire engine from Poplar Fire Station attended.