The Queen handed out awards at a reception for the Royal Life Saving Society (RLSS) more than 75 years after achieving her own medal in the pool.
She greeted volunteers and representatives of the drowning prevention charity at Buckingham Palace on Tuesday to mark its 125th anniversary.
The monarch, now 90, was 13 when she achieved her Life Saving Medal from the society, of which she is the patron.
Two photos of the Queen as a teenager, one showing her in the water rescuing another swimmer and a second with the medal pinned proudly on her swimming costume, were posted on t he Royal Family's official Twitter feed.
The Duke of Edinburgh and Prince Michael of Kent, the charity's president, joined her as she presented three prestigious honours on behalf of the society.
Trained lifeguard Tyler Bailer, 17, from Canada was given the Russell Award for saving his stepfather's life by using CPR.
And Professor John Pearn, from Australia, was awarded The King Edward VII Cup in recognition of his lifelong contribution to researching drowning prevention.
Zac Dominic, from St Lucia, was also honoured with the Mountbatten Medal after risking his life to save a man who was being dragged out to sea by the current.
The Royal Life Saving Society was founded in London in 1891 in response to hundreds of unnecessary drownings in the UK.
Its founder William Henry intended to teach lifesaving and water rescue skills to those using the River Thames.
Now, the charity estimates around 400 people die from drowning in the UK every year.
Earlier in the day, Prince Michael had visited the Royal Over-Seas League in London and presented certificates to volunteers from RLSS member branches throughout the Commonwealth.