Michael Phelps has ended his swimming career on a fitting high, adding a final Olympic gold medal to his impressive collection.

The American swam in Team USA's winning 4x100 metres medley relay squad to pick up his 18th gold and 22nd Games medal overall since his debut in Sydney in 2000.

Six golds and two bronze medals in Athens was followed by his historic eight gold medals in Beijing four years later.

As he stepped out into the poolside ahead of the race, even Phelps himself appeared emotional, echoing the sentiment of thousands of fans worldwide.

He swam the butterfly leg, handing over to Nathan Adrian in first place for the freestyle as the United States clinched yet another title in three minutes 29.35 seconds