Teddington RNLI witnessed the lock keeper falling into the River Thames and was able to rescue the man immediately.
Teddington RNLI volunteer crew were returning from a demonstration at the Walton Viking Sea Scout Festival when they saw the lock keeper fall backwards into the River Thames.
The man had been assisting another vessel under tow, when he tripped and fell into Sunbury Lock.
Teddington volunteer helmsman, Tim James, said: “We were waiting for the lock to empty, watching the lock keeper assist a vessel under tow, when he tripped over a bollard and fell backwards into the lock.”
He continued: “Thankfully he was wearing a lifejacket and we were perfectly positioned to drive straight over and help him out of the water.”
When the crew of the D-Class lifeboat reached the lock keeper, they found he had inhaled some water and injured his neck.
Volunteer crew members Matt Ellins and Ray Searles administered first aid and monitored the man closely until the ambulance arrived.
When the ambulance arrived, the crew provided a full handover of the incident and treatment.
The shaken lock keeper was taken to hospital for observation.
The incident happened at 2.30pm on 9 July.
Helmsman James added: “Half of the drownings in the UK and Republic of Ireland are accidents. It is so important to keep yourself safe and wear a lifejacket when around open water.”