Lewis Pugh from Plymouth covered the length of the English Channel
Mr Pugh was campaigning for better protection for oceans across the world. He's calling on the government to protect at least 30% of the world's oceans by 2030.
The endurance swimmer started his mammoth challenge from Land's End and 49 days later, he finished his swim in Dover, Kent.
He was stung by countless jellyfish along the way, and damaged his shoulder too. His wife Antoinette says it's been very difficult being away from him.
The environment secretary Michael Gove was among the crowds who welcomed him after completing his epic journey.
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