Olympic kite surfer Bruno Lobo -- who just competed at the Paris Games in August -- heroically saved a drowning swimmer last week ... and the dramatic rescue was all captured on video.

Lobo posted the footage to his Instagram page over the weekend ... explaining to his thousands of followers the scene played out on Jan. 10 -- as he was testing some new gear during a surf sesh off a coast in Brazil.

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The vid shows as Lobo was making his way through the waves ... a young woman appeared to be in serious distress as she was swimming through some choppy waters.

Lobo thankfully saw her and was able to slow down and grab her. She hopped on his back ... and the two eventually made it to shore safely.

The woman seemed unharmed ... and gave Lobo a hug before she walked off with what appeared to be friends and medics.

Lobo was heralded as a hero in the comment section of his post ... and he responded to all the love by saying, "I only did what needed to be done and what was within my reach!"

Lobo -- who competed in the Men's Kite event at the Paris Games over the summer -- was able to reunite with the swimmer on Monday ... and after taking pics together, the woman's family wrote in a caption on the flicks they're "forever grateful" to Lobo for his actions.