LONDON — A British man who spent five months at sea is believed to be the first person to swim around the island of Great Britain, making his way back to land in Margate, a coastal town in southeastern England, on Sunday.

The swimmer, Ross Edgley, 33, had not been ashore since June 1, when he set off on his 1,780-mile aquatic journey.

Sunday morning, he was welcomed ashore by loud, enthusiastic cheers.

“It still doesn’t feel real,” Mr. Edgley told the BBC.

For more than 150 days, Mr. Edgley swam six to 12 hours a day. He spent the rest of his time eating and sleeping on his support boat, from where he documented his quest in episodes streamed online.